I am not an expert but he looks all yorkie to me. Maybe the vet was a little put off by his weight. I read a little history behind yorkies and I discovered that the original yorkies were actually largest than today's yorkies. By the way, welcome to YT
! But the cat vaccines would be a red flag to me and I would be thinking the breeder may not be so very honest. There's nothing wrong with a mixed breed but the breeder should have been honest . I would be concerned if I was charged for a full breed if he is not.