Creepiest thing I've ever seen on a game??

Okay guys, so I'm playing DayZ and roaming around the coast trying to help survivers. when suddenly i see about a dozen men wearing clown masks and playing Tiny Tim's "Living in the Sunlight" and it was probably one of the scariest things I've ever witnessed in a video game. Can anybody please tell me what was going on??

Skip to the last 3 or 4 minutes to see what was happening

https://www.youtube.com/watch?v=U54K1aF324w