I think what he was getting at is a firework intercepting a quadcopter will revector its trajectory.
Someone had already planned every path the fireworks were to take, so the spent shells would not land at the wrong place.
However, having hit a quadcopter, a live firework, its payload yet to be spent, could have its trajectory revectored to a viewing area, with likely tragic consequences.
Someone designed that thing to go off a hundred feet up, not spuzzing around under the seats of the audience because it hit something on the way up.
I am sure the safety of the quadcopter was the least of their worries... it is that deflected live firework that I would be worried about.