I suspect Denbrock knows that Leonard has the yips on long balls and he was trying to give him a layup. NIU sold out to defend the run (this is why there were only 15 running plays, can't run into an 8 or even 9-man box), the WR was open, and anything better than an absolutely, completely terrible throw would have been completed. Hartman would have hit that throw, and so would Coan. Leonard should have hit it.
I think Denbrock's play calling was defensible, unless he knew that Leonard was going to miss that badly (which is possible, I suppose).