I pass by armored cars on a fairly regular basis at several of the grocery stores and shopping centers I visit. I make it a point to make eye contact with the driver and or side guard and give them a calmnod.
I have been watched closely before (cant blame them really) but I have never had YOUR kind of experience.
Kudos to the store manager if he did indeed tell the guy to take a hike. Like someone planning to rob an armored car would carry their weapon out in the open like you were. :quirky