As far as detractors...somebody could have just as easily poked fun at Guy#1 (mock dancing, throw a soft object at him, etc.), thus invalidating his own self-absorbed ecstasy, and probably making it more difficult for the observers to be converted into participants (not to mention detracting from the overall mood of the purpose of the festival).
I think a more reasonable explanation for how participation precipitated would be to look at it from the perspective of influence and the time for that influence to propagate throughout the crowd. Guy#1 takes a few minutes to influence Guy#2 to join. The two dancing together takes less time to influence Guy#3, and then the three of them take VERY little time to attract a small group, and then the whole festival jumps in...
I think that there is some value in calculating the time it takes for the group to go from one participant to many participants to see if there is an exponential growth rate taking place.
That might take the effort out of squinting too hard.
;)