[Koss]

If he wont raise an overpair I doubt he's going to raise a pair of aces on the flop vs. a preflop raiser. He'd probably call down with A9 here. That's why this raise confuses me. He could certainly have 2 pair, or maybe he raises a draw? Whatever, small pot, an overcard to your pair, facing aggresion, no shame in folding.