It looks like the operators of the display had everything preloaded into mortar tubes and pre-wired to a computer controlled junction box (replacing the old fashioned "nail board"). Someone entered the wrong timing interval between shots (like 0.1 second rather then 10 seconds) into the computer. You will notice that the individual fireworks did not all go off at once, the show played out at an accelerated pace but was still individual shots.
Back when their were people running from tube to tube, lighting fuses with a railroad flare, I recall a shot were someone dropped a flare into the powder magazine. There was an enormous fireball silhouetting a running figure beating cheeks like the devil was right behind him. No one was injured but they all needed fresh laundry...
Regards,
GtG
Bill Cabot: What’s the t-shirt say?
Depot Worker: “I am a bomb technician, if you see me running...
[laughs]
Depot Worker: ... try to catch up.”