as far as i know, nobody from the AT class of 2009 was involved. in the hiker parade, you line up according to the year you hiked, so at most, two classes would have been hit (but everybody's kind of smooshed in together, so it's unsurprising that the guy was able to hit 50+ people at one time). as far as i've seen so far, they haven't released names or anything (not that real names would help much regardless. most people only know your trail name unless you were close enough friends to keep up after the trail), so i don't know for sure. but everything i've heard from my friends that were there was that nobody from 2009 was involved.
it's really horrible though. i mean, they say it was just a terrible accident. i'm sure it wasn't intentional. but the entire festival is just one big relaxing, fun time. and the hiker parade itself is just one big giant water balloon fight with the people who live in damascus. a car running through a giant crowd of people is the absolute last thing that would be on anybody's mind.