Rig Veda II.36.5 says
eṣa sya te tanvo nṛmṇavardhanaḥ saha ojaḥ pradivi bāhvorhitaḥ |
tubhyaṃ suto maghavan tubhyamābhṛtastvamasya brāhmanādā tṛpat piba ||
Translation of Ralph T.H. Griffith is as follows:
This is the strengthener of thy body's manly might: strength, victory for all time are placed within thine arms. Pressed for thee, Maghavan, it is offered unto thee: drink from the chalice of this Brahman, drink thy fill.
Translation of H.H. Wilson (p.183) is as follows:
This (libation). Indra. augmenter of thy bodily (vigour). favourable of old to the resistless strength of (thy) arms: it is effused. Meghavan. for thee. it is brought to thee from the Brahmana. do thou drink and be satisfied.
Both the translations are giving the meaning of from brAhmana. Though the word बरह्मा - brAhman was mentioned in II.1.2, it indicates the Almighty. However, here the word brAhmana was used.
In Rig Veda X.90.12, बराह्मण - brAhmana was used indicating one from Varna system, along with kshatriya, Vyasya and Sudra.
However, in the mantra in question, the word brAhmana alone was used that to requesting Indra to take oblation from a brAhmana.
I don't think it was used with the meaning of Varna system.
Can anyone throw light, please?