That's a very strange board to just push the flop like that. There's an awful lot cheaper ways to "make you" fold. If I had Aces and I was him, I'd do a nice $45 or so bet to keep the action going, but not commit myself with a possible set or something. Looks to me like he tried to pick off your $4 and is now trying to make you go away.

Were you really aggro in preceding hands? If so, this may be a set, considering your line is an obvious KK or AA.

I think you actually might be ahead here.

Then again I don't play 100NL, so what do I know?