I agree with you, but it's just ignorance or laziness from the actors most likely. Are there people responsible for handling the props and the firearms? Yes. Are they right 99.99% of the time? Probably. Does that mean the actor should just trust these people all of the time? No.
People make mistakes and one way to help mitigate those mistakes is by making sure you practicing proper gun safety as much as possible. Whether basic gun safety is or isn't common on sets doesn't matter a whole lot to me. This incident demonstrates that it should be something any person handling a firearm should be aware of, even if they're on a movie set.
I'm by no means a gun expert, but I also dislike how "prop gun" or similar things are being thrown around. It's not a fake, toy, prop, etc. if it can actually fire. It's a real gun and should be treated appropriately. I don't really understand why they don't find a less deadly alternative for some of these scenes.