Could be. It's been years since I've heard of anyone doing this. But might be how he shows/proves your not an employee since your "renting" the truck from him.
Mayfield Express (Buno's outfit powered by Sundeck, whatever "powered by" means), at least at one time, I don't know if they still are, charged rent for things like ratchet straps and other securements, as a means of being able to insist they have no employer-controls over those who drive for them. There is no actual tax basis for doing this. A $25 weekly truck rental fee is a money grab. And, unless there is a separate rental agreement, or the agreement isn't spelled out int he lease, adding a rental fee could put the owner at a much greater liability risk than if the fee is not present. The owner could be held liable for the renter's misuse, unsafe use, or reckless use of the equipment unless such terms are expressly enumerated in the rental agreement.