So who ran from the store? I hope you did not shop there. I would have asked the **Assistant M.** if he had the authority to eject me for lawful conduct? And if he stammerred and stood there dumb founded, would have excused myself to go shopping until he or another manager actually ordered me to leave.
I would follow up with a letter to the manager informing him that you objected to the bizzarre treatment from teh assistant manager and expect to shop there again while open carrying & to please provide a copy of the coprorate policy banning **customer** carry, if there is a such a policy, so that you can post it to the world wide web.