In my humble opinion, safety is never off topic. This looks like there were several break downs in communication. The guy on the front didn't know what was going on in the back. The guys in the back had no idea what was going on in front. And the Chief of Piece WAS FREAKIN' ALSEEP! He is the one in control of that gun. He needs a few days bucked and gagged to give him time to think it over. He obiously did not have his crew properly trained.
At reenactments when I am drilling my crew I will sometimes mix up the commands on purpose. I tell people over and over that we are all responsible for safety and anyone can call, WAIT or DON'T or HOLD at any time if they see, or feel, that something is wrong and unsafe. So I might, in drill without cartridge, call "WORM" after "Prick & Prime" and hope to God I get a "WHAT?!?! WAIT! THAT'S WRONG!"
Or maybe call "Fire" before I call "Ready! Clear front!"(our signal for the cannoneers to step away from the piece and cover their ears. They are supposed to echo it back to let the person on the lanyard know that everyone is clear of the piece and it is safe to fire). I would rather have the gun not fire because #4 didn't hear everyone say Clear, than to have the gun fired when people are not ready. Awareness, awareness, awareness.