From the rulebook:
https://operations.nfl.com/the-rules/2019-nfl-rulebook/
From the Rulebook:
The ball belongs to the defensive team at the spot
where the player’s foot or other body part touched the ground to establish possession. If that spot is in the end zone, the result of the play is a touchback, even if the ball is not on, above, or beyond the goal line.
So, it's true it's not where the ball is. Which seems odd to me, but there it is.
But I would have thought it was the *second* foot that established possession, and that was the toe tap on the 1 yard line ( or so ).
But then again, with all the going to the ground garbage, you could say he only "established possession" rolling out of bounds.
SECTION 5 SAFETY
ARTICLE 1. SAFETY. It is a Safety:
...
Exceptions:
It is not a safety:
...
(2) If a defensive player, in the field of play, intercepts a pass or catches or recovers a fumble, backward pass, scrimmage kick, free kick, or fair catch kick, and his original momentum carries him into his end zone where the ball is declared dead in his team’s possession.
The ball belongs to the defensive team at the spot where the player’s foot or other body part touched the ground to establish possession. If that spot is in the end zone, the result of the play is a touchback, even if the ball is not on, above, or beyond the goal line. (11-6-1)