Not a pilot here but a builder so I'm limiting my comments to that. It is not uncommon for a structure to fail in stages, especially when the initial stress has caused large-scale structural damage to adjacent stressed members. In this case just the reverberation from the band's amplified sound or from dancers in rhythm could have caused just enough vibratrion to make the rest of the structure fail as shear forces were aggravated or displaced parts shifted. And if wood was involved, it often delaminates relatively slowly as opposed to snapping in two, even without additional stress loading being applied. It could have been failing slowly even without any other aggravating input after the initial settling under the strain. Of course the structure was never designed to accept this load so it seems to have done very well and performed admirably and normally. Having nothing else to add that's it for me in this thread.