I guess he's probably check-raising the turn as well if he has a hand as big as KJ910 etc.. with the

plus another spade.
I think you played the hand right and made the correct play, we're essentially turning our hand into a bluff catcher, when he bets the river its a big bet near enough the pot, so what can he be doing it here with, his bet is kinda fishy to me and it looks liek he is trying to represent that he is bluffing....but I'm 100% sure that more times than not he has the goods.
good fold.