It wasn't in this article, but another article on the incident mentioned that earlier in the year, there was a large group of students from Oregon State University who had a similar party weekend. The difference was that 40 of them stayed an extra day to clean up and haul out trash.
In that situation, it took just a small minority of people to clean up the entire mess of the large group. I have no idea if this is something that had been planned from the start but I can see how just a few principaled individuals deciding to clean up could inspire folks who maybe felt bad but didn't want to make a fuss to stay and help out.
The actual name: Full self driving (supervised) is so shady. Supervised is just a less crappy sounding way to indicate that you will have to take over and drive sometimes. So sometimes the car drives itself and sometimes you drive. So partial self driving, partial human driving. I'm surprised they didn't call it "Partial Full Self Driving". That would certainly amp up the trolling factor and really separate the true believers who would come out defending it with Olympic level mental gymnastics.