People who steal things aren't just "called" thieves. They are thieves. In some cases, they can even get away with not paying for gasoline (or other things), not get caught, never get called a thief, yet they still are, definitionally, thieves.
Depends on whether you assume the background property arrangements are valid. We call them a thief because we call this gasoline owned by this group of people we call a company.
Some other group of people might call everyone who buys gasoline thieves since they profit off of the negative externality they leverage on the rest of society.
It's all a matter of what you view as neutral and objective and what you view as a violation of others rights.
