I think its close between a call and fold on river. If you think about what hes doing that with, its a very narrow range. Hes not doing this with KQ AK, there are no straights, or flushes out. You said he may be too aggressive? Maybe he can do this with 8c9c? Ac5c? I think when you call the turn bet, he could put you on one pair and figure that you cannot stand the river action? Otherwise he is doing this with weird 2 pairs and sets and the line he took in this hand doesnt really add up. I would have looked him up and just made a note, but I tend to get curious when someone's line looks funny. Although I think folding is definately okay without a solid read.