Yup, he has the right to it. There's part of the V5 registration document (V5C?) that you're supposed to take which proves you own it, while the rest of it gets sent off to DVLA, car gets re-registered in your name, and new V5 makes it's way to you. That's why you don't hand money over unless there is a V5...that, or it could be stolen, and again, you've got no proof of ownership