I'd have to check, but IIRC they were very close to land. The fight that follows is where Sokka looses his sword, and that was over land. Those super-zeps are also shown to be extremely slow, so they wouldn't have gone far in the time in between.
That wasn't Aang, that was the avatar state combined with the spirit of the sea. We know that the Avatar as a whole can be bloodthirsty - indeed, the previous air Avatar was quite willing to kill.
The other killing actions by the rest of the team I'll grant you: Sokka and Katara certainly aren't as pacifist as Aang. Not so sure about Aang dropping the normal zeps, though - he merely punctures them, they might have had enough air for a semi-controlled fall similar to that of the Boiling Rock (compared to Katara's sliced-the-bag-in-half move).
A better example was mentioned earlier: the tanks that he dislodges during the Air Temple attack would not have been in any way designed to drop, unlike aerial vehicles which could have had something off-screen. I suspect, though, that if shown, they would all hit conveniently deep snow drifts.
Grey Wolf