There's a lot of speculation and armchair-experting on the internet around this. I won't venture to much of my own opinion since a) I'm not an expert and b) there's still a lot we don't know.
I will make a couple of observations:
It appears that there are multiple points of failure here.
From what 'experts' on the internet have said, it seems that there's an industry-wide expectation of safety and what that consists of, but different approaches to arrive at more-or-less the same place. One thing that seems to be universal on all sets is that there should never be any live ammunition on set. Ever. If that rule had been followed, it massively reduces the chances of injury.