If you've already nicely explained the law, sometimes the best response is just "ok", and walk away. Hard to argue with that.
Also, IMO it is more correct to say something like "OC is not prohibited by any law and is specifically protected by Article 12, Sec. 3 of the MS Constitution." HB2 had nothing to do with OC, it merely defined CC to mean fully concealed, and specifically listed visible, holstered firearms as an example of a firearm that was not concealed. It kinda helps people understand the whole "open carry law" nonsense.