Since the manager told you "NO" you need to go back during the day and speak to the store manager. Since it was around midnight the manager you spoke to was probably the grocery manager (head stock boy). Tell the store manager what happened and that you know Harris Teeter's corporate policy is to allow open carry. I am sure his tone will change. You will be welcomed with open arms into the store and please do not write corporate about your negative encounter with the night time flunky.
If he defends the managers decision or he was the one that was present tell him thanks for his opinion and you will be forced to contact corporate, the NRA and GRNC. HT tried to pull the posting thing a couple of years ago and it lasted for about 2 weeks till the NRA and the Charlotte area residents went to their azz. This fiasco is well documented on OCDO.