Originally Posted by
mrdeux
As the over wing exits are the small escape doors, it would almost certainly have been opened by a passenger.
At least some 767-300s have cabin crew stationed by the overwing exits. I know that's the case on ANA (toilet in front of the first overwing, with 2 CC seats on the back wall/by the first door, divider between the exits, normal passenger seat aft of the second exit). Not too sure about the AA 763, seatmaps suggest this isn't the case there.