I wouldn’t be surprised if they come back this week and admit they got it wrong (though it’s the NFL, so probably not).

Here’s the rule.
1. Player Going to the Ground. A player is considered to be going to the ground if he does not remain upright long enough to demonstrate that he is clearly a runner. If a player goes to the ground in the act of catching a pass (with or without contact by an opponent), he must maintain control of the ball until after his initial contact with the ground, whether in the field of play or the end zone.

His initial contact with the ground was his knee. He clearly had control of the ball. He then stretched across the goal line while on the ground because he hadn't been touched. They got it wrong after reading their own rule.