[Mister Z]

I'm assuming he's a decent player, and is somewhat paying attention to Nap here...

He would've 3-bet with AA, KK, QQ, AK, and maybe JJ - I think those are out of the equation. After the flop he has to have you on AA or KK if he has a read on you being a non-overly-aggressive player. The turn raise then rules out AQ. He knew he had at least 3 players going to the flop for at least 2 SB a piece so he probably thought he had odds to chase his set with his 44 or 33. That's my pick.