I would make a serious complaint about this vet and hope you did not have to pay him anything because he does not know a thing about snakes.
That being said, the bp might have an RI. What did he mean by, no external signs of an RI? Like the snake had no symptoms? Too bad you won't know what else the snake has, mouth rot, parasites, etc, etc. YOu can pretty much expect that people give snakes away that are very sick and you gotta be ready for it.
Make sure you quarantine this guy from your other snakes or you will be stuck with lots of sick snakes.
Good luck.