Fair points. I was mostly thinking of situations like downloading using a separate device, writing to a usb drive or SD card and installing via that. Downloading an installer and using it is just downloading without using an app store.
I’ve always took side-loading to mean installing from local storage, as opposed to downloading from remote storage. As far as I’m concerned downloading from a third party app store should not be treated as side-loading.
Do you know that he didn’t take a gun safety course? For all we know, he could have had plenty of knowledge on how to safely handle a firearm and simply decided to ignore it for the sake of looking cool. The fact is that no amount of safety training can stop someone who decides to do something stupid.
I absolutely agree with your last point though. There should be extensive training in how to handle a firearm safely required before someone can buy a gun.
Progress towards what?