I think it would depend on the facts of the situation, but I think one example would be this: If someone is receiving a car from a third party and they're not paying to use that car, then it would be reasonable to assume that there is some sort of quid pro quo in that situation, some reason why that car is being provided.
I think it would be a question of fact, whether there's some link with the employer that would make it reasonable to conclude that the car is being provided because of the employment relationship.