They were in shotgun formation using a silent count. Corbett told Allen to snap the ball with the hand signal the Rams were using all game long. And Allen did
exactly what he was supposed to do.
Clearly, Stafford wasn't ready for the snap but it is equally clear that Allen wasn't to blame. Something broke down in the communication between Stafford and Corbett. But Allen bears no responsibility as far as I can tell.
It's pretty clear in this video. Corbet signals just 4 seconds in and then all hell breaks loose:
At the 53 second mark you can lip-read Stafford saying "I never lifted my leg.". I can't see who he's talking to, but I bet it's Corbett.
AlbaNY_Ram