I don't have any statistics or sources for this but I am willing to bet big that most folk who call 911 when they see OC are not wanting to "harass" a law abiding gun owner. I believe they are not used to seeing someone carrying around a gun in public and so they are frightened. With the incidences of mass killings and spree murderers that keep being broadcast by the media I think their fear is explainable.
We had a dim-witted kook here in Nashville who walked about a suburban nature park in military style cammies with an AK-47 handgun configuration slung over his shoulder scaring the heck out of the bird watchers. Park Rangers were called and he was released after questioning. Later, the idiot walked down the middle of Belle Meade Boulevard (ritzy part of town) carrying a pistol openly in his hand. Police were called and later this numbskull sued the police and park rangers for "violating his civil rights".
I'm not hard core in calling for the anti gunners to be punished, I'm mostly expressing a frustration level with them making life uncomfortable for other law abiding people, just because they feel uncomfortable.
Your anecdote is certainly one which calls for caution. I don't disagree. However, there was also an instance in Virginia, I believe, where several guys were in a restaurant OPEN CARRYING which was the only way to LEGALLY CARRY in an establishment which served alcohol, IIRC. Some one got upset with them, not because they were acting threatening or anything. As a matter of fact, if I recall the story, they had been there for quite some time before some imbecile got upset and decided to contact the police. It gets pretty tough when laws are written, law abiding citizens follow the law as they were written, yet still get hassled by authorities because some nincompoop "FEELS" uncomfortable around guns. The guns were in holsters. I think those gun owners rights were violated much more so than the dummy who called the cops. It riles me to read stories like that, just as much as it upsets me to read stories like yours. Which one is more common? I don't honestly know.
So, the question remains, what recourse do the law abiding gun owners have when they are singled out by anti gunners and the anti gunners call the authorities on them. It's almost slander to a degree. False police reporting? False accusations? What should be done? Nothing? Like health care reform, we can't just do nothing.