Not really. Many more people involved made this all occur by not following all the rules in place, so it can't be 100% on him. The person or people who brought the live ammo on set and the Armorer (who is ultimately suppose to be in charge) are more responsible.
There's plenty of case law about joint liability. Two people can separately be fully responsible for both criminally and civil liability for the same incident where it's impossible to determine fault.
An example I remember from years ago was a person was injured and lost his eyesight by two hunters firing birdshot at the same target at the same time. It was (then) forensically impossible to determine which gun - or perhaps both - the pellets came from so both were held equally liable.