I was told the story about a similar disaster. The control board for the fireworks had banks of mechanical switches that had to be tested in advance by an electrician, before being hooked up to the fireworks. Everything was tested and the reset switch was not switched to reset the system. When they turned on the system to begin the program, it caused everything to go off at once.
Most of these big civic fireworks displays have systems ran by a computer. I can imagine the complexity involved and what happens when the operator makes one mistaken mouse click. BOOM!
I was figuring that it was controlled by a computer running Windowssomethingoranother, and it encountered the red, white, and blue screen of death.