Pre 4b 100%. Flop B150 16% B75 77% B33 6%. Turn B33 100%. AS played turn with B75, River X 100% XF 100%. If the turn B33 called then River XC 77% XF 23% all AA for a B33 by villain.

Preflop - good Flop - good Turn - good River - I think this is a bet. The reason for checking is to use AA as a bluff catcher, but villain probably doesn’t have a lot of bluffs. It seems much more likely he has Qx or some other medium strength hand that would like to get to showdown as cheap as possible.