Tim, I only somewhat agree with you. Trying to recover from a mistake like that is very difficult, if not impossible except with very very experienced drivers.
HOWEVER, I think about what he did (moving the shifter in a "U" pattern) and it just does not make logical sense to me. 4th gear to 3rd gear requires going across the gate, but 4th to 2nd requires one weird freaking shift IMO. I have mis-shifted before, right before a curve, but I did not lose the rear end (of course I was going about 60 mph, not 100 mph).
If it was me, I would take the lumps for my own mistake, and not blame it on an instructor. Also, I seriously doubt the insurance company will pay for squat since he was at the track. My $.02.
Davy