I agree with all ong said.
Except I'd point out that he not only donk bet OTF with a tiny blocker bet, he did it in a 4-handed pot. Risky at best to try to donk bet a blocker against 3 opponents.

Your flop bet put Villain in a position to call 8 into a pot of 49 (which would have been a lot more if either of the other villains had called). Excellent odds for just about any drawing hand, and you have AA, so he is almost certainly the one on a draw.