i have watched this play a couple times, but the angle doesnt show it well enough. although I would have to say it looks to me like he was hurt after the fact as he was attempting to do some sort of celebration immediately after the sack.... it was a very very strange look sequence of events.
however... if this would help get rid of this stupid ass rule (it will certainly increase injuries as people try and make awkward tackles) Yep, IMO he was injured trying not to fall on Carr!