Nonsense, from a simple read of all the articles of the past year, according to Seth Kenney, the owner of the prop-shop used by the production, and txt messages he received from Guiterriz-Reed (before the shooting incident) - Live ammo was brought on to the set, and Hannah Gutierrez-Reed used the live ammo in the prop guns for live firing tomfoolery/ target practice ....

I'm guessing it's the armorer's fault. Diversity hire (her father was a renowned armorer), she'd only done one movie before that, and there were gun safety incidents on that set as well.

Yet another case of a woman being told she can do anything and fucking it up.