Once upon a time there was a parking lot attendant. He watched a person getting out of his car and could have said, "You're not allowed to park in that particular spot." But the attendant stayed silent. For he was not an employee of the owner of the parking lot, but rather of the towing company, whose financial interest was in towing cars that were illegally parked.
The parking lot owner's interests would have been served better by an immediate oral notice to the driver, since the car would have been removed faster.
I happen to know of a case where a criminal charge of trespassing was dismissed because an employee of the company on whose property the defendant was said to have trespassed watched him for some time without ever telling him to leave.
Might something similar apply to the situation described here, if the car's owner sued the towing company, saying the attendant's silence implied consent?