...They are in their uniform, but I assume they are working in the capacity of private security.
I would assume this... If he is in a police uniform, he is a police officer. If he is in a security uniform, he is security, but he can make a full arrest being a sworn LEO and more or less "transition" to a police officer (he would just need a phone booth to change in - LOL) when the need arises.
I have encountered many districts that will allow a company to rent a cop (not "rent-a-cop"), which is where a LEO can take on optional additional duties off-duty or for overtime, whether it is security for a clinic, bank, or public event that requires a visible security presence and the LEO agency is not responsible for maintaining an official presence. The agency benefits by renting officers out, the officer gets overtime, and the company needing security benefits by having a fully sworn LEO instead of just a security guard. Your encounter sounds just like that to me. This is only what I have been exposed to, so that may or may not be the case in your district.
I don't think I understand something from your posting though... were you carrying concealed or open? You said he saw that you were carrying.
If it was open carry, he shouldn't have even said anything to you unless he wanted to be conversational, address a legal infraction, or if he enforces some bank policy denying access to the building with a weapon (which he ruled out by stating he didn't know if the bank had a problem with it). You wouldn't have to justify your possession of a firearm to anyone for any reason.
If it was concealed, then I would understand if he asked you if you had a CCW (the issue of requiring you to produce it is another thing), but stating that he hoped you were a cop was completely inappropriate on his behalf. It does more than imply that he feels you shouldn't be carrying unless you're a cop, which is just wrong, statutorily, and being on the job, wearing his uniform, this is at the minimum misbehavior on duty. He can have his personal opinions off-duty. Also, have you considered that if you were carrying concealed, your firearm should have never been visible and the entire encounter may have never been more than saying "Hi" on the way through the doors, plus the bank tellers should never have known you were carrying from any of your visits? I'm not trying to be argumentative. Everyone making statements is essentially an armchair quarterback/lawyering and presenting consenting or opposing views of what you've stated. I'm saying that hindsight is 20/20 and we can all learn from things like this so we don't do the wrong thing in the future.
Regardless, I'm glad your encounter went well overall and no one had to be a jerk, and as you said you may very well have to meet this guy again in the future, so you want to be on favorable terms.
For the others chiming in on this, I'm in Nevada, and you don't need a CCW here to have your weapon in the car, visible or not (
Link Removed) except in the Las Vegas area, where they enforce laws that can't statutorily exceed the State (the district laws are perpetually under review for repealing to comply with State law). I'm assuming your areas make a big deal about carrying in your car, then putting on when you exit your car?