Easily avoided... just a call to the police beforehand and a call when the guns were showing up on set would have had these filmmakers rolling instead of spending hours not filming while they sorted out stuff that should have been thought ahead.
Sometimes common sense evades, and it's a bit disheartening, the focus to film (this BTW, is why I don't say I'm shooting something) overrides that little voice in many filmmaker's heads that says good things like: "Perhaps waving a gun around in a liquor store where the public can see us is problematic."
And the teaching staff should have read the script and brought it up as well. This never should have happened. They can "laugh about it now", but as a producer, I'd be pissed about the delay in production. As a teacher, I'd be worried about the lack of concern over this event by those involved.