I had the exact same thing happen to me shortly after working on my clutch. I was having a problem with my banshee accelerating and determined it was a bad clutch. I replaced it and took it for a test ride and it just gave loose and I didn't even feel it happen, it just was like it was in neutral in every gear. The locknut came loose due to the fact (I think) that the huge nut (32mm or something) which I don't know the name of being loose. The guy that put my banshee back together before me forgot to use the lockwasher. That was supposed to be torqued to 90 N*M and I could spin it with my fingers. So I am guessing that your locknut came loose and let the friction/clutch plates open up(I don't mean the 32mm one I mean the small locknut on the outside). I could be wrong, just trying to give input.
EDIT: Holy crap I just realized that you live in Frackville. You mean like close to St. Clair? I live around Schuylkill Haven.