It wasn't really an "event", it was just a dune trip which was talked about on the internet between friends. Why would we need a permit to go to the dunes and have some fun at the hill? Just because it is talked about on the site, it doesn't mean it's any different than going out on Halloween or anyother weekend. Nobody can legally be held liable if someone got hurt.
Even still, I have asked the BLM in the past about permits when it comes to big group trips. The only reason you need a permit is if it is an organized, sanctioned event where it is a competition. There is no registration, no money collected, and no organized races. It's just like any other dune trip, but with some lights.