Dude don't sweat it. First of all, if his transmission did not have the update kit installed in it then things are just different from yours. Whole different updated detent wheel and shifter stuff; front torsional damper bearing probably installed backwards, not to mention both of the bearings are different in yours. I've been on these sites for years and never heard of this happening to any rocket. I think it too was not fully in neutral and popped in gear. If he had not been revving the tits out of it, it probably would be fine. It's unfortunate but it can be fixed or like I said stuff another engine in her.
Oh and so everyone is clear: when your gearbox gives up, trying to ride it easy down the road or home or to the exit will only increase the damage and the price of the rebuild !!!!!!!!!!!!!!!!!!!