it's a theory.When all you do is pass the ball, you're going to put up huge numbers. That doesn't make it mean anyone's a great QB. Secondarily, if you watched the games, you'll see a lot of yards were given up between the 20's. Then when Purdue got in the red zone, things changed. Yards between the 20's are pretty meaningless when you don't score points.
In reality, the stats were pretty darn good... TDs to INTs, especially.
If all you do is pass, a defense is going to catch onto that pretty quickly...