Maybe they're religious too, unable to cope with the beauteous randomness and perfect common chaos of reality.

Not sure why you need to have to drag religion in to this but that aside,

I can't think of anywhere I've been more than once that is like that. Participants tend to sit in the same places. Regulars generally know what is "in keeping" and what isn't for the event. In a session, if someone starts a tune, others will take this as a cue to join in. A "random chaotic" happening of someone striking up a tune when another one was playing would (unless the "culprit hadn't heard it) be considered rudeness. No one is likely to repeat a song or tune that has already been done, etc.

Of course there may be no written rules but rather than random chaos, I would suggest there is a fair degree of social interaction and understanding,