Doesn't look that weird to me. He is just checking it down blocking to keep you from pounding the river. I'd bet it's a decent jack (JT, JQ) or king with kicker trouble, possibly a middle pp that wants to showdown (your only hope).
If you play std, the flop hit a good portion of your range and he's oop so happy to keep the pot small. But he has enough to call you down and block the river.
I'm not sure how aggressive you are with top pair or better, but this wasn't played very strong at all. Looks like a whiffed flop and a half-hearted follow up or a weak piece of it. Not a strong hand looking for value. He's not looking for you to fold, he wants you to pay him off or outkick him for cheap. You have almost no FE if you raise this river. I lol if you flip the 9 here, and definitely float and call you light all night. Call for metagame and adjust. Hope he writes something like 'donk: bets 2 streets and calls with 3rd pair.'
