Borrowed vehicle passenger damaged door, who pays?

Hello, I describe here an incident of my couseng since we are not quite agreeing who is right. The following problem arose, he borrowed his mother’s car and took a passenger with him. He in turn hit the door unintentionally when the passenger door in a parking lot against a broken stone. The result is a damage of approx. 150€ for a new Mercedes door :/ Well the question: he says it has to come up with the car Vk for what would result the car The passenger has no PHpV! My couseng however has a PHp boxplus from axa, in which it is called extra of course he was not the one who opened the door, but another sentence says that the driver is responsible for the safety etc. and now I would point out this sentence of the insurance “They cause damage to rented, borrowed or leased things. BOXplus offers insurance coverage here, while conventional private liability insurance does not pay in such cases. What do you think about this? Thank you already in advance for your Help