1) A quality airsoft gun looks exactly like a real gun. That's the point of them, good simulation. They're lucky he didn't return fire.
2) If the law pertaining to paintball guns applies, it's assault with a deadly weapon (detached retina = no fun). If it was a wal-mart gun, the the odds are very low it would do more than just sting for a few seconds, but built-up airsoft guns can break 400fps no problem.
Little bastards deserved it. I'm biased though. I see it as stupid kids doing stupid things that can lead to legislation against fun, perfectly-legal hobbies. They deserve the punishment, and need to be very thankful one or more of them didn't get killed.