as the hand was played on your end he can effectively eliminate Qx from your range. You are not going to check/call the flop and then check the turn again flopping top pair here. So i infact do like his line from the opponent because the way your hand was played you basically turned yoru hand face up and make it known that you had some kind of middle pair along with a draw. With the river being an Ace that is 100% a brick card for your hand and so knowing that your opponent definitely made the right move betting this river. Your river call here also is definitely questionable however it just so happened that your opponent was holding 100% air here. As played your opponent very easily could have A9/A7/A6 type of hand here and is betting that river for value once he hits his two pair on the river.