Based on the info that (M)EH, the driver, went to USC in Columbia, I'm going to guess that Jason Doe went to Carolina & bummed a ride based on a sticker on the van or gamecocks hat or something. I think the Carolines either were girls from USC, too, or from Queens College (now Univ) in Charlotte & recognized (M)EH either from hs or a college party.
I think it's highly possible that JDoe borrowed some clothes from (M)EH after hooking up to head back to school. A likely scenario to me, given my friends at that time in college who would head out for a long weekend of Dead shows, but were by no means "Dead Heads," would be something like this:
JDoe goes w/ group of ppl from college (USC?) not necessarily friends, but ppl he knows who connect via a "Ride Board." (Remember, we did not have the internet or cell phones, so ride boards were often how you got away for the weekend from college.) They intend to crash with friends of friends, hang out on their own at the shows, and meet back up at X time at Y location to head back to school. JDoe might be running late, so they all head back & figure he caught another ride without really thinking it was a big deal. Nobody was really friends in the first place, so nobody really thinks much of him not showing up or following up later. Things happen, no big deal. We did this all the time. You pay the driver a few dollars to let you ride along wherever. We always assumed it was safe b/c we "went to school together" even if we didn't know the ppl at all.
JMO, but seems pretty likely to me.