It says passing grades, so I'd assume at least the designed runs are taken out. There were a lot of drops, and from what I know of PFF those count for the QB almost as much as if they were caught. But yeah, 68.5 seems high.. and definitely feels like that shouldn't ever be the 5th best in the conference. There were some baaaad games though:
Sitkowski (Rutgers): 8/19, 40 yards, 0 TD 1 INT
Lewerke/Lombardi (MSU) 18/48, 220 yards, 0 TD 1 INT
Coan (Wisconsin): 9/20, 60 yards, 0 TD 2 INT
Thorson (NW): 15/30, 122 yards, 1 TD 2 INT
Blough (Purdue): 20/31, 142 yards, 1 TD 0 INT
I think they also get less credit for short passes that the receiver turns into a big gain, so a drag route that goes for 60 doesn't pull up their rating much. But at a glance, Bush's 11/25, 126 yards, 0 TD 2 INT doesn't seem a lot better than the list above.