Yeah, this one is exceptionally bad not just for a vet, but for anybody with any claims on chickens. Newbies starting out with fad chickens know better than he does!
That vet is full of 💩 , as others have already explained. It's really unfortunate that misinformation like this is coming from a "professional", and I can't blame somebody for trusting a "professional" - after all, that's how it should be, in an ideal world. But that's not how it is in this...