[Larude]

His most likely holding indeed is KK or QQ with a club (than it would make sense to call the turn). But he could also have TT with a club for the same reason. A pair of jacks would also be reasonable but then you might expect him to raise on the turn because he can't put you on a flush (unless you have KQs). He might also gone in with a relative trash because he thought you wanted to steal, dont know how reasonable this option is. In any case i don't think he will call your river bet when beaten so a check is just fine.