In college football, is throwing your helmet off before the play is over not a penalty?

It would have been if the play existed. The flag was thrown in back corner of endzone by corner ref with two seconds left. Whistle was blown at :01 upon snap you just could not hear cause of the crowd. the play was dead before it started. Plus he threw his helmet off after he downed ball with no time left. No matter what a game cannot end on defensive penalty anyways