I am on the same page as O. Pureheart.
Start with the video at 1:41. Note, the QB releases the ball from the B-12. Note, the just-released ball obscures the far hash mark designating the B-12. Then, A54 first contacts the ball at the B-12.25; hence, backward.
Remember, by rule the pass does not have to be truly backward. It just has to not be forward. So, even if A54 first touched it at the B-12.0, it would be considered a backward pass.