Clearly a legal play in that respect, because the rule states that as long as any part of the body is behind the LOS, it's a legal forward pass. Pretty much beyond dispute that was the case here.
In any event, though, does any of it really matter? Perhaps, but it would have put Auburn at 2nd and 15 at our 44-yard line. Still no guarantee they wouldn't have scored, I'm afraid. Auburn would have still had 32 seconds and 3 timeouts, so they could have possibly gotten another 6 or 7 plays in.
If that is the rule, I can say definitively it has been called erroneously many times. Not sure, is the rule the same in the pros? Because although I have seen it called, I can't remember whether it was college or pros.