Hmmm... is the off-duty Fireman in danger of being charged with anything?"Well, it wasn't illegal" is not a statement that should be made by responsible citizens or mature adults as a way to justify or rationalize a moronic act.
If the rifle wasn't illegal, seems like he should be. Otherwise, anyone open-carrying (anything) could be subject to being held at gunpoint until the cops arrive. We can't have it both ways.
And stupidity by itself isn't a crime. :/