Well they make sure that cast members are safely indoors before they receive the all clear to begin fireworks so it is unlikely that it would result in any injuries. Also the roofs of nearby buildings are fireproofed so the fireworks are safe to perform. just this time, the tree wasn't too lucky
Fireworks falling like this are usually expected once in a while. It's even worse when people have to manually light the fireworks. During the 4th of july here, there are always one or two that decide that they want to go up and come right back down.