Here is the definition of a touchback from the NFL --
Touchback: When a ball is dead on or behind a team’s own goal line, provided the impetus came from an opponent and provided it is not a touchdown or a missed field goal
Now a safety --
Safety: The situation in which the ball is dead on or behind a team’s own goal if the impetus comes from a player on that team.
In other words, it's only a safety if the team with the ball goes backwards INTO their endzone and is then tackled (or loses the ball out of bounds, or receives certain penalties, like intentional grounding).
Source(s):
NFL referree rulebook
The key to defining whether a play results in a safety or not is called "impetus" by the NFL. Two points are awarded to the opposing team if the impetus for why the ball has been called dead on or behind a team's goal line came from the team originally in possession of the ball. Offensive examples include a player being tackled in the end zone after retreating into it or committing a penalty in the end zone. One of the more common occurrences of a safety happens when a punt is blocked out of the end zone.
Read more:
What Is A Safety Call In A Football Game? | LIVESTRONG.COM
Can one of the rules gurus answer this?
All I can guess is that Whoadirty is right. The zebras thought that the ball accidentally, inadvertently or by the Patriots "impetus" crossed the goal line. I don't see how they could think that but maybe I misunderstand the rule. Can someone enlighten me?