Go look at the teams he faced towards the end of the season. Drake, KSU, Baylor, Kansas, and Texas Tech. Not exactly murderers row! Against Texas he was bad, very very bad. We tend to let players slide on a game or two however we generally dont take into account the defenses played when kids do well.
This year will tell us more about Purdy. I have a feeling hes going to look awfully good for the next month and a half (may struggle against TCU, I'm still figuring that team out) and then come November when Texas and OU hit the schedule we will see how good he really is.
This happens with QBs everywhere by the way. At Iowa, Stanley can look like a stud one game, then like a JV player the next. That guy pisses his pants against Wisconsin every single year!