I wasn't going to make a post to keep some sort of mystery around this but I figured why not.
As I understand it, this was actually caused by one of the artists haha.
They thought it was a funny little thing so showed others in the studio so a lot of the staff got on and had a big hat party.
I don't think this was on the live server though haha.
(We have different builds of the game to test things before letting everyone play changes)
Funnily enough, we were talking about this video in studio the other day when this was posted talking about how funny it would be to put it in the live game for a little bit haha. Don't think it would happen but can still dreammmm!