Is the concept of Gandhabba Brahmanical teaching?

MN 93 has the following discussion:

"'But do you know, masters, if the mother who bore you went only with a brahman, and not with a non-brahman?'

"'No, master.'

"'And do you know if the mothers of the mother who bore you — back seven generations of mothers — went only with brahmans, and not with non-brahmans?'

"'No, master.'

"'And do you know if the father who sired you went only with a brahman woman, and not with a non-brahman woman?'

"'No, master.'

"'And do you know if the fathers of the father who bore you — back seven generations of fathers — went only with brahman women, and not with non-brahman women?'

"'No, master.'

"'Do you know how there is the descent of an embryo?'

"'Yes, master, we know how there is the descent of an embryo. There is the case where the mother & father have come together, the mother is fertile, and a gandhabba is standing present. The coming together of these three is the descent of the embryo.'

"'But do you know for sure whether the gandhabba is a noble warrior, a brahman, a merchant, or a worker?'

"'No, master.'

"'That being the case, do you know who you are?'

"'That being the case, master, we don't know who we are.'

The above teaching questions two things:

1. How do you know if your mother slept with a non-Brahman (i.e., had an extramarital affair)?

2. How do you know if the sperm your mother received was non-Brahman sperm (from the above extramarital affair)?

This teaching has nothing to do with reincarnation. The teaching explicitly asks how can you know who your mother slept with & what she bore?

Shame on so-called 'Buddhists'. Shame. How shameful the superstition, which the Buddha condemned (in MN 95). Shame.

Shame on Thanissaro for slandering the suttas by including "[the being about to be reborn]" into the sutta translation. Shame.

From MN 93 (though translated by Sujato, I replaced "spirit being reborn" with "gandhabba"), the sentence in question is:

An embryo is conceived when these three things come together—the mother and father come together, the mother is in the fertile part of her menstrual cycle, and the gandhabba is present.’
Idha mātāpitaro ca sannipatitā honti, mātā ca utunī hoti, gandhabbo ca paccupaṭṭhito hoti; evaṃ tiṇṇaṃ sannipātā gabbhassa avakkanti hotī’ti.

Pretty much in Buddhism and Hinduism, Gandharvas are a kind of musician devas . According to the wisdomlib page on Gandharvas:

A Gandharva (Sanskrit) or Gandhabba (Pali) is one of the lowest ranking devas in Buddhist theology. They are classed among the Caturmaharajikakayika devas, and are subject to the Great King Dhrtarastra, Guardian of the East. Beings are reborn among the Gandharvas as a consequence of having practiced the most basic form of ethics (Janavasabha sutta, DN.18). It was considered embarrassing for a monk to be born in no better birth than that of a gandharva.

Gandharvas can fly through the air, and are known for their skill as musicians. They are connected with trees and flowers, and are described as dwelling in the scents of bark, sap, and blossom. They are among the beings of the wilderness that might disturb a monk meditating alone.

As stated in the Hinduism.SE answer linked by Dhammadhatu in his comment, Kandarpa is another name for Kamadeva, the cupid god of Hinduism, from the wisdomlib page on Kandarpa:

Kandarpa (कन्दर्प).—Another name for Kāmadeva. Kāmadeva was born of the mind of Brahmā and as soon as he was born he turned to Brahmā and asked "Kaṃ darpayāmi?" (Whom should I make proud?) So Brahmā gave him the name Kaṃdarpa alias Kandarpa.

It doesn't make sense that a Gandharva is present for conception.

It could make sense that cupid (Kandarpa) is present for conception, so this is the first hypothesis from me. Of course, cupid here could be a personification of romantic or sexual passion. So, this could just mean that sexual passion is present.

From the wisdomlib page on Gandharvavivaha or Gandharva marriage, we find:

Gāndharvavivāha (गान्धर्वविवाह):—The Gāndharva marriage (vivāha).—This is a marriage arising out of the voluntary union of a maiden or her lover which springs from desire and has sexual intercourse for its purpose. It can be compared with the modern love marriage.

Based on the definition above, once again, "Gandharva" being present, could just mean sexual passion being present.

From the wisdomlib page on apagabbha, we read:

apagabbha : (adj.) (apa + gabbha) not destined to another rebirth; (a + pagabbha) not haughty.
(Source): BuddhaSasana: Concise Pali-English Dictionary

Apagabbha, (adj.) (a + pa + gabbha) not entering another womb, i. e. not destined to another rebirth Vin.III, 3. (Page 50)
(Source): Sutta: The Pali Text Society's Pali-English Dictionary

From this page (quoted from Max Mueller's book "Vinaya Texts"), we see that this comes from the Vinaya, where the Buddha said:

He who has freed himself, Siha, from the necessity of returning in future into a mother's womb, and of being reborn into new existences who has rooted out (his being subject to) rebirth, and has done away with it, as a palm tree is rooted out, so that it is destroyed and cannot grow up again - such a person do I call apagabbha.

So, if "apagabbha" means one who is not destined for descending into a womb, then presumably "pagabbha" means one who is destined for descending into a womb i.e. being to be born. It's possible that "pagabbha" became changed into "gandhabba".

So, these are my two theories:

1. "Gandhabba being present" just means sexual passion is present.
2. "Gandhabba being present" was originally "pagabbha being present", meaning the one who is to be born is present.

The second theory originated from Andrei's comment on gabbha.

‘But do you know
‘Jānanti pana bhonto—

for sure whether that spirit is an aristocrat, a brahmin, a merchant, or a worker?’
taggha, so gandhabbo khattiyo vā brāhmaṇo vā vesso vā suddo vā’ti?

This part nullifies the first theory, so we are left with the second i.e. "gandhabba being present" was originally (probably) "pagabbha being present", meaning the one who is to be born is present.

This is probably the same meaning as "sambhavesi" in the Karaniya Metta Sutta which according to the wisdomlib page on sambhavesi means:

sambhavesī : (m.) one who is seeking birth. || sambhāvesi (aor. of sambhāveti), esteemed; honoured; mixed with.
(Source): BuddhaSasana: Concise Pali-English Dictionary

It simply means one who is to be born.

The OP asked whether there is a spirit or soul or being that is born or reborn?

If one answers "yes", that would eternalism. If one answers "no", that would be annihilationism.

According to SN 23.2, there is the definition of "being" as follows:

As he was sitting there he said to the Blessed One: "'A being,' lord. 'A being,' it's said. To what extent is one said to be 'a being'?"

"Any desire, passion, delight, or craving for form, Radha: when one is caught up there, tied up there, one is said to be 'a being.'

"Any desire, passion, delight, or craving for feeling... perception... fabrications...

"Any desire, passion, delight, or craving for consciousness, Radha: when one is caught up there, tied up there, one is said to be 'a being.'

There is another definition of "being" in SN 5.10:

Why now do you assume 'a being'?
Mara, have you grasped a view?
This is a heap of sheer constructions:
Here no being is found.

Just as, with an assemblage of parts,
The word 'chariot' is used,
So, when the aggregates are present,
There's the convention 'a being.'

It's only suffering that comes to be,
Suffering that stands and falls away.
Nothing but suffering comes to be,
Nothing but suffering ceases.

So, there is a being in Buddhism, but it's not eternal and it is constructed dependent on conditions.

The concept of "rebirth" in Buddhism is simply the continuation of suffering beyond death. There is no eternal person or being or soul or spirit or consciousness or self that dies and is reborn. In fact, it's not even the same being or person or consciousness throughout a single lifetime. It's always changing.

However, looking at the context of the sutta, the Buddha simply wanted to prove that there is no such thing as caste from birth.