What you describe sounds like a parking lot attendant, not loss prevention and you have no basis to suggest that you have any right to park or wait anywhere on their property when they tell you not to. If police had been called you possibly could have been arrested and your car impounded for refusing to move. Not only can they dictate where you stop, but some businesses can also require that you not loiter in your car. For example, casinos frequently will not allow anyone to sit in their car while parked in their lot.
Your tag number could possibly be used for a police report or for future reference maybe to tow, give you a trespass order or whatever. The point is that you are a guest on private property and must either follow directions, leave or face potential consequences.

