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Reported speech of crowds is not precise. It's not like a whole crowd would only say one sentence repeatedly, unless they were shouting a slogan, which is not the case here. Many variants of the same "Who does he think he is?" surprise and anger would have been expressed.

It is, however, curious, as Luke usually emphasises the women more than the other gospel authors.

Kadalikatt's answer points out that Matthew has the crowd mentioning both parents.

Why, in the Gospel of Mark, is Jesus referred to as the son of Mary but, in the Gospel of Luke, he is referred to as the son of Joseph?

One good reason would be to distinguish that Mary was the Mother of Jesus physically; while Joseph was in terms of Jewish Law the Father of Jesus, even if this is only in a legalistic sense.

When Jesus was an adult, people often referred to Him as the “son of Joseph” (Luke 4:22; John 1:45; 6:42), although the gospel writers were careful to maintain that Jesus’ true Father was God, with Joseph being more of a foster father or stepfather (see Luke 3:23). People also referred to Jesus as “the carpenter’s son” (Matthew 13:55), suggesting that Joseph worked as a carpenter or some other type of handyman (the Greek word for “carpenter” could also be translated as “stonemason” or “metallurgist”). Whatever Joseph’s particular vocation was, it is evident that he worked hard to provide for his family, doing what he could to help Jesus grow in “wisdom and stature” (Luke 2:52).

Joseph isn’t mentioned in any of the stories of Jesus’ adult ministry, while Mary His mother occasionally is (Mark 3:31; John 2:1; 19:25). The absence of Joseph in the stories of Jesus’ ministry has led many to believe that Joseph died sometime between when Jesus was a young boy (Luke 2:42) and when He launched His public ministry as an adult (Luke 3:23). The fact that Jesus, as He was dying, committed the care of His mother to John gives strong indication that Joseph had indeed passed away by that time (John 19:26–27). - Who was Joseph, the father of Jesus?

Jewish law recognizes only the male lineage to the house of David, this is the reason Luke mentioned that Joseph was the father of Jesus. This way Jesus could take the royal title of King David.

Nevertheless some have even thought that Mary, herself was from the house of David.

How can Jesus Christ be called "son of David", if the Blessed Virgin is not a daughter of David?

(a) If by virtue of Joseph's marriage with Mary, Jesus could be called the son of Joseph, he can for the same reason be called "son of David" (St. Augustine, On the Harmony of the Gospels, II, i, 2).

(b) Tradition tells us that Mary too was a descendant of David. According to Numbers 36:6-12, an only daughter had to marry within her own family so as to secure the right of inheritance. After St. Justin (Adv. Tryph. 100) and St. Ignatius (Letter to the Ephesians 18), the Fathers generally agree in maintaining Mary's Davidic descent, whether they knew this from an oral tradition or inferred it from Scripture, e.g. Romans 1:3; 2 Timothy 2:8. St. John Damascene (De fid. Orth., IV, 14) states that Mary's great-grandfather, Panther, was a brother of Mathat; her grandfather, Barpanther, was Heli's cousin; and her father, Joachim, was a cousin of Joseph, Heli's levirate son. Here Mathat has been substituted for Melchi, since the text used by St. John Damascene, Julius Africanus, St. Irenæus, St. Ambrose, and St. Gregory of Nazianzus omitted the two generations separating Heli from Melchi. At any rate, tradition presents the Blessed Virgin as descending from David through Nathan. - Genealogy of Christ

This is where taking note of the very first verse Mark writes (in his gospel account) throws some light on why Mark wrote what he did in 6:3.

"The beginning [arche, Heb. 6:1] of the gospel of Jesus Christ, the Son of God." (Mark 1:1 KJV)

At the outset, Mark's identification of Jesus Christ as the Son of God provides the basis for understanding all other statements made about him. Only once the reader has accepted this identification, will all other points about who Jesus really is, make spiritual sense.

Mark's focus, from the very first words of his book, is the Messenger of the Covenant, the ministry of the aphesis of sins. That is why it's important to see the point Mark makes in chapter 6 verses 1 & 2, prior to this cry of disbelief. Bear in mind that Christ was assigned to preach "To the Jew first", to his own people. Here is an explanation from this book:

"Notwithstanding the Jews being of the seed of Abraham; irrespective of their springing from the stock of Israel; despite that they were Jews, faithful to the throne of David: when Jesus went with the gospel 'to the Jew first', he found few enough of the children of promise that could be counted for the seed, for all the multitudes that were born after the flesh.

Never was this more conspicuous than when in 'his own country', Mk. 6:1. The irreconcilable difference between the children of promise and the bondchildren became more evident than ever. Here appeared a divine distinction that prevailed over all, and would endure world without end.

'Is this not the carpenter [the son of Mary]?' they cried. 'And they were offended at him.' But Jesus said unto them, A prophet is not without honour, but in his own country, and among his own kin, and in his own house, Mk. 6:3,4. 'And he marvelled because of their unbelief', Mk. 6:6. And as it was with those in particular, so it happened with the Jews in general.

Nevertheless this gospel was 'to the Jew first', and thereunto was he sent. And he called unto him the twelve, and, empowering them, sent them forth into all the land, two by two. 'And they went out, and preached that men should repent', Mk. 6:12" Mark, pp. 123-4, John Metcalfe

This quote shows why Christ's detractors stressed him being "son of Mary" - because they had already taken offense at him, they would not consider any link to the line of David. Had they seriously considered the possibility that he could be the foretold Messenger of the Covenant, they would have taken into account the significance of Joseph's lineage to the line of David.

So, the answer is that it is not Mark who is choosing to put a different stress on this by emphasiszng Mary (compared with Luke's stress on Jesus and Joseph). It is the disbelievers in Jesus being the Messenger of the Covenant who betray this by speaking of Mary, when they could have spoken of Joseph. Mark's stress through all of his writing is that this Jesus is the Christ, the Son of God.

Luke 4:22 puts it like this:

And all bare him witness, and wondered at the gracious words which proceeded out of his mouth. And they said, "Is not this Joseph's son?" (Luke 4:22)

Mark 6:3 puts it like this:

Is not this the carpenter, the son of Mary, the brother of James, and Joses, and of Juda, and Simon? and are not his sisters here with us? And they were offended at him.

Matthew 13:55 puts it like this:

Is not this the carpenter's son? Is not his mother called Mary, and his brethren, James, and Joses, and Simon, and Judas?

In fact, the wording "the carpenter" as used by Mark , in another way of saying "the Carpenter's son" as used by Matthew, given the trend of passing down of the "family trade" from father to son, that prevailed in those days. So, one should read Mark 6:3 and Matthew 13:55 with the same comprehension.

Hope this explains the problem!