My reading of the rule is that the Referee had to determine that the player would not have gone to the ground and it was only his choice of diving to the endzone (which would then also be a football move). I think that would have been a bad determination.
But, from his wording it seems to imply that the going to the ground happened after he crossed the plane and as such was no longer part of the consideration. However, I think it still had to be (in order for the catch to have occurred). This would be somewhat similar to finding that someone who dove from the 1 yard line and caught the ball in the air but continued to fly through the air and first contacts the ground out of bounds has nonetheless scored a touchdown because the act of touching out of bounds occurred after crossing the plane with the ball and thus ending the play.
Even though the event that causes it to not be a catch occurs later then the event that causes it to be a touchdown it is nonetheless a necessary event.