I wouldn't have stopped betting. By your description I had him on AA. (Since that is the best hand and it can't be beat ;-) or so a new player would think. or at best 88 for trip 8s or 55 for trip 5s on the flop.

No way would I have even thought running 3s would give him quads.

I bet now you would have a) have a read on him and b) taken all his money.