When a fumble goes out of bounds in the end zone, the following shall apply:
If a ball is fumbled in the field of play, and goes forward into the opponent’s end zone and over the end line or sideline, a touchback is awarded to the defensive team; or
If a ball is fumbled in a team’s own end zone or in the field of play and goes out of bounds in the end zone, it is a safety, if that team provided the impetus that sent the ball into the end zone (See 11-5-1 for exception for momentum). If the impetus was provided by the opponent, it is a touchback.
so by rule it should have been a safety. we still should have won the game but those extra 2 points and the ball could have ended things right then and there I believe.