I don't have stats, but it appears that the reason Holtz has not thrown the ball downfield is because of the high percentage of INT that Higgins is getting off of his downfield passes. I heard an NFL analysis talking about QBs state that "accuracy is something that a QB either has or doesn't. It is not something you can teach a QB. What a QB does learn is timing with receivers and placement of the ball."
What I am seeing is a QB is just puts the ball up every time he throws it down field and isn't trying to place the ball. Whether that is because of a bad offensive line or because he is inaccurate is still TBD.