Either way, the ball was not blown dead (which is a judgment of the officials) and the player threw the ball down backwards as he approached near the 10 yard line. This is not an illegal pass; this is a backward pass which would make the play still live. The video was really hard to tell where the lines were. But the officials did not stop officiating and ruled this a TD.
I guess the Referee should have had a conversation with the two officials that were standing right there and everything would have been resolved.
Peace