Why is this music chosen for a Catholic Mass?

This music that you think of as 'concert music' was originally church music.

I don't recognize the specific piece in the video, but pieces of a similar style were originally written to be used in church services. Most classical music with "Mass" or "Requiem" in the title (or linguistic variants such as "Missa" or "Messe") were intended to be used in celebrations of the Mass. This includes works by Haydn, Mozart, Beethoven, Verdi and Bach among many others.

The words being sung are actually the prayers said during mass, and the sung versions are used in place of the recited prayers.

The music is commonly called choral or church music, and has been part of Catholic and other traditions for many centuries. These settings require a high quality choir to do well, so you will usually hear them only in larger churches and cathederals - and with changing musical tastes they are only infrequently used even there. But there is absolutely nothing unusual about using this style of music in church, and singing it in church was the original intention.

Why is this music chosen for a Catholic Mass?

I hear music in this style quite often in the Extraordinary Form of the Mass. Almost always uniquely at very solemn occasions only.

Before getting into the music part of this question, I would first like to put a few things into perspective.

November 23rd in the Extraordinary Form of the Mass was solemnly celebrated by the Swiss Cardinal Lars Anders Arborelius O.C.D.. Cardinal Arborelius was created a Cardinal by Pope Francis on June 28th, 2017.

Sacred music elevates the spirit and our earthly senses towards higher levels such prayer, adoration and the sacred truths of our faith. This is why Gregorian Chant plays such a vital roll in the sacred music in the Mass of Pope Pius V.

The so called “concert music” that you refer to is not that at all. Such music as seen in your video is quite common and is done as a way to make the celebration of the Mass more solemn. Such music is generally termed as choral music or choir music.

The choir and its’ choir master in question are performing a valuable liturgical function and are trying to elevate the dignity of the Sacred Mass regardless if some of the faithful would in fact consider it concert music. They are performing a sacred act and enhancing the the sacred liturgy with great music even if some are unsure of what it is.

A choir (also known as a quire, chorale or chorus) is a musical ensemble of singers. Choral music, in turn, is the music written specifically for such an ensemble to perform. Choirs may perform music from the classical music repertoire, which spans from the medieval era to the present, or popular music repertoire. Most choirs are led by a conductor, who leads the performances with arm and face gestures.

A body of singers who perform together as a group is called a choir or chorus. The former term is very often applied to groups affiliated with a church (whether or not they actually occupy the choir) and the second to groups that perform in theatres or concert halls, but this distinction is far from rigid. Choirs may sing without instrumental accompaniment, with the accompaniment of a piano or pipe organ, with a small ensemble (e.g., harpsichord, cello and double bass for a Baroque piece), or with a full orchestra of 70 to 100 musicians.

The term choir has the secondary definition of a subset of an ensemble; thus one speaks of the "woodwind choir" of an orchestra, or different "choirs" of voices or instruments in a polychoral composition. In typical 18th- to 21st-century oratorios and masses, chorus or choir is usually understood to imply more than one singer per part, in contrast to the quartet of soloists also featured in these works.

Liturgical function

In addition to leading of singing in which the congregation participates, such as hymns and service music, some church choirs sing full liturgies, including propers (introit, gradual, communion antiphons appropriate for the different times of the liturgical year). Chief among these are the Anglican and Roman Catholic churches; far more common however is the performance of anthems or motets at designated times in the service. - Choir (Wikipedia)

As I mentioned already Gregorian Chant is not the only music sung in the Old Rite. It does however take presidency over other forms, but it does not have a monopoly on sacred music. Motets may be sung at times.

In western music, a motet is a mainly vocal musical composition, of highly diverse form and style, from the late medieval era to the present. The motet was one of the pre-eminent polyphonic forms of Renaissance music. According to Margaret Bent, "a piece of music in several parts with words" is as precise a definition of the motet as will serve from the 13th to the late 16th century and beyond. The late 13th-century theorist Johannes de Grocheo believed that the motet was "not to be celebrated in the presence of common people, because they do not notice its subtlety, nor are they delighted in hearing it, but in the presence of the educated and of those who are seeking out subtleties in the arts".

Medieval examples

The earliest motets arose in the 13th century from the organum tradition exemplified in the Notre-Dame school of Léonin and Pérotin. The motet probably arose from clausula sections in a longer sequence of organum. Clausulae represent brief sections of longer polyphonic settings of chant with a note-against-note texture. In some cases, these sections were composed independently and "substituted" for existing setting. These clausulae could then be "troped," or given new text in the upper part(s), creating motets. From these first motets arose a medieval tradition of secular motets. These were two- to four-part compositions in which different texts, sometimes in different vernacular languages, were sung simultaneously over a (usually Latin-texted) cantus firmus that once again was usually adapted from a passage of Gregorian chant. It is also increasingly argued that the term "motet" could in fact include certain brief single-voice songs. The texts of upper voices include subjects as diverse as courtly love odes, pastoral encounters with shepherdesses, political attacks, and many Christian devotion, especially to the Virgin Mary. The vast majority of medieval motets are anonymous compositions, and there is significant re-use of music and text. They are transmitted in a number of contexts, but were most popular in northern France and Paris; the largest surviving collection is in the Montpellier Codex.

Increasingly in the 14th and 15th centuries, motets made use of repetitive patters often termed panisorhythmic; that is, they employed repeated rhythmic patterns in all voices—not only the cantus firmus—which did not necessarily coincide with repeating melodic patterns. Philippe de Vitry was one of the earliest composers to use this technique, and his work evidently had an influence on that of Guillaume de Machaut, one of the most famous named composers of late medieval motets. - Motet (Wikipedia)

Another form of sacred music is of the polyphonic style.

In music, polyphony is a type of musical texture consisting of two or more simultaneous lines of independent melody, as opposed to a musical texture with just one voice, monophony, or a texture with one dominant melodic voice accompanied by chords, which is called h*m*phony.

Within the context of the Western musical tradition, the term polyphony is usually used to refer to music of the late Middle Ages and Renaissance. Baroque forms such as fugue, which might be called polyphonic, are usually described instead as contrapuntal. Also, as opposed to the species terminology of counterpoint,[clarification needed] polyphony was generally either "pitch-against-pitch" / "point-against-point" or "sustained-pitch" in one part with melismas of varying lengths in another. In all cases the conception was probably what Margaret Bent (1999) calls "dyadic counterpoint", with each part being written generally against one other part, with all parts modified if needed in the end. This point-against-point conception is opposed to "successive composition", where voices were written in an order with each new voice fitting into the whole so far constructed, which was previously assumed.

The term polyphony is also sometimes used more broadly, to describe any musical texture that is not monophonic. Such a perspective considers h*m*phony as a sub-type of polyphony.

Western Europe and Roman Catholicism

European polyphony rose prior to, and during the period of the Western Schism. Avignon, the seat of the antipopes, was a vigorous center of secular music-making, much of which influenced sacred polyphony.

It was not merely polyphony that offended the medieval ears, but the notion of secular music merging with the sacred and making its way into the papal court. It gave church music more of a jocular performance quality removing the solemn worship they were accustomed to. The use of and attitude toward polyphony varied widely in the Avignon court from the beginning to the end of its religious importance in the fourteenth century. Harmony was not only considered frivolous, impious, and lascivious, but an obstruction to the audibility of the words. Instruments, as well as certain modes, were actually forbidden in the church because of their association with secular music and pagan rites. Dissonant clashes of notes give a creepy feeling that was labeled as evil, fueling their argument against polyphony as being the devil’s music. After banishing polyphony from the Liturgy in 1322, Pope John XXII spoke in his 1324 bull Docta Sanctorum Patrum warning against the unbecoming elements of this musical innovation. Pope Clement VI, however, indulged in it.

The oldest extant polyphonic setting of the mass attributable to one composer is Guillaume de Machaut's Messe de Nostre Dame, dated to 1364, during the pontificate of Pope Urban V.

More recently, the Second Vatican Council (1962–1965) stated: "Gregorian chant, other things being equal, should be given pride of place in liturgical services. But other kinds of sacred music, especially polyphony, are by no means excluded.... (Vatican II, Constitution on the Liturgy, 112–18) Religious singing by the people is to be skillfully fostered, so that in devotions and sacred exercises, as also during liturgical services, the voices of the faithful may ring out”. - Polyphony (Wikipedia)