It is very important to understand and use proper terminology. A snap can not be fumbled. If it is passed (backward) directly and immediately by the snapper, it is a ball loose from a backward pass. It it comes loose during the attempt to hand it, it becomes a backward pass, and is a ball loose from a backward pass. If a player attempts to gain possession of the ball, loose from a backward pass, touches the ball, but fails to gain possession of the ball, then the ball is muffed and remains loose from the backward pass.
Neither a snap (hand to hand or a backward pass), nor a ball that is not in player possession, can be fumbled.
When discussing rules, we should always use proper terminology.