My two (fairly uninformed) cents: I lived in a dorm adjacent to where Joshua lived when he disappeared. I happened to be invited to a (different, I think) party at Metten court the night he went missing and decided not to go because it was November in Minnesota and the walk between "the tundra" (near our dorms) and Flynntown (near Metten) was a damn cold walk that time of year.

I've always assumed that someone with ill-intentions offered him a ride back to the dorm to save the ~5-minute walk in the cold. It's a ride I probably would have accepted from a stranger on a campus that always felt safe to me up to that point.