I think you should have increased the size of your bet on the turn so you could figure him out. In general such a small bet (relative to the pot size shows weakness). My guess is that he had tt-qq, or aqs. Because after seeing your weak turn bet he decided to try to out play you on the river since it pretty obvious that neither of you have the king. I think, and correct me if I am wrong, most people can smooth call the flop but tend to wake up on the turn. Anyways tough hand.