i will admit that neither term fits perfectly- but alas, if he was acting like a tool I'd charge him with whatever my supervisor told me to, and let the DA sort it out.
"Assault also is any intentional act or threat of action that reasonably causes a person to feel afraid of impending violence—such as pointing a gun at someone
La. Rev. Stat. Ann. §14:36
This is sketchy, but if someone says "it scared me the way he walked in with that gun in his hands" - you're in trouble. In NC it was called "Brandishing in a Menacing Fashion" - holding or carrying a firearm in a manner inconsistent with your environment. At low ready in a gun range- fine. At low ready in taco bell- crime. I don't think LA has a brandish law, and if so I don't recall ever hearing about it in either my limited legal or law enforcement backgrounds.
You are flirting with a law suit by thinking that way. It doesn't matter if an open carry firearm "scares" someone if the OCer didn't intentionally threaten that person. I think the best resolution would be to check with the business owner/ manager and ask if they allowed firearms. If not the OCer must leave, or they could be charged with remaining after forbidden. I am not a fan of OC in general, and despise the low ready rifle OCers, but it's their right. Other factors such as aggressive posture, confrontation initiated by the OCer, or unsafe handling of the firearm changes things.