Well let's see, pre-flop he's probably limping pretty wide, let's go all pairs 22-JJ (QQ-AA would probably raise, although maybe they don't), Ax, all broadway, 54s+, 86o+, etc. What of that bets the flop and what of it checks? It depends on how passive he is, this guy is fairly aggressive so he probably bets all of his aces, 66-JJ, his 8x and 5x, maybe 76 or flush draws also, but those could get checked back too. He probably checks back his air too, although many players would fire their air here.
After he checks, the turn peels a 9, which completes 76 and gives draws to T6 and JT, so when he just calls our bet, based on what we thought he checked back on the flop he's calling with mostly draws I'd say. Which brings us to the river... I mean, it's not impossible for villain to have A9/AQ/99, flopped sets, etc. here, but you'd think those hands would be played a little bit faster, so those are more unlikely. Still though, it just seems to gross to flat when we're only afraid of one hand, so basically I'm not really sure. I probably would have 3-bet the river also, btw.