Very nice shot, I managed that in a few occasions too but no, I don't have proof because I don't record matches.
It's very hard yet doable unless the chopper is moving fast, in my opinion.
The one I'm most proud of is sniping a quad moving at full speed in the distance, but I know that was luck and I'll never get a kill like that ever again, I wish I had recorded it.
The best part of sniping the pilot is that sometimes the other guys on the chopper don't undertand what's going on or are too slow to switch seats and they crash lol.