They're posturing and after money.
On paper there are plenty of safeguards. In reality of a hectic movie set, the gun expert prevails when all these items fail. There never should have been live rounds loaded.
Ask yourself, in your job there's the 'published' procedure then the 'real world' one. In scenario #2 who holds more blame the actor, who is be definition an actor, or a trained/certified firearms wrangler.
If this prosecution stands then the atty general should prosecute each and every workplace accident where some random, untrained, uncertified person could have _maybe_ prevented a tragedy instead of the professional whose sole job was to prevent it.