[Abbaddabba]

Why would anyone in his situation checkraise the river with a better hand?

I think you have one of the worst hands that he would expect you to value bet the river with if checked to that you could conceivably have, and even with that you are considering checking behind. Anything better on the turn, and it's going 4 bets earlier.

I'd expect him to have some one pair type hands like Kx or Ax, checking with the intent to fold and occasionally calling out of desparation.