Why shouldn't the airport operator try to protect itself?
It can do that through the courts. They do not need to resort to wild west justice. Especially if you are talking about a company that can be easily located.
If the crew shut the doors and called for pushback clearance I think the airport would have been in some trouble legally.
This could have also been a poker game with the airport seeing what they could get away with knowing their actions were 100% illegal.