Interesting discussion. I was very pleasant with the guard despite very gently and respectfully questioning the policy. He was quite professional and pleasant as well. I feel he didn't personally care what I did, so I don't think this is a case of a rogue guard.
It is
definitely the case of a rogue guard, or of one who had been misinformed. His demeanor is beside the point. What if he had wanted to confiscate your equipment- would you have let him? It would not have mattered how pleasant or professional he was.
He violated your rights. A security guard does not have the powers that a cop does. And a cop would have had no right to violate your constitutional rights to be there, doing what you were doing.