I saw a lot more than "sparks". It looked like a couple of freakin blow torches starting that fire.
Yes, it climbed the wall and started spreading across the ceiling rather quickly..but the band was still playing during the video..they were not trying to put it out until it was already out of control.
Anyone who's witnessed fires knows that they can flare up and spread incredibly fast...even without an accelerant present...and can kill a person quickly.
I saw a friend of mine catch fire, and it spread from his legs to the top of his head in a few seconds. He panicked and started to run, I knocked him to the ground and put him out in about 5-10 seconds. And he was still so critically burned that he spend over 2 months in the hospital..had to have skin grafts etc.
I don't know how unreasonable it was for this fire to spread so quickly in a open space.
But I do know the band is responsible for setting it.
Those weren't blowtorches. That was the back wall igniting from the sparks. Went up so quickly many people on the scene probably mistook the burning wall for pyrotechnic torches.