Strange indeed. My only thought is that maybe he put you on a weak tens-full boat that he thought you might lay down if he came over the top of you and tried to put you all in. I doubt it though, because if he had half a brain he would have seen that you were so pot-committed at that point that you almost certainly would call.

Man, I know it's annoying to get slow-rolled and sucked out, especially when you think you have the nuts, but you really did play the hand better than he did. A lesser player would have pushed in a nanosecond in response to his bet on the river. Any bad beat in NL that leaves you with at least some of your stack isn't as bad as it could be.