If his hands/arms were over the line but didn't touch the ground, it's not a foul. If that were a foul, you'd have to stop 5 feet in front of the foul line when you released the ball so that your hand didn't cross the line, vertically extended to the ceiling.
As to whether it would be a foul even if he did, I'll have to look at the rule book to see when the frame is technically over. Is it over once the ball has gone off the back of the lane and is now a "dead ball?" If it is, that might mean it wasn't a foul after all (similar to me throwing a shot, waiting 2 minutes, then walking back up to the foul line and stepping on it), but then again, most intentional fouls are committed after someone sees their result. So I don't know.
Either way, in that situation, I'm not saying a word other than "congratulations."
Jess