There isnt a local branch of that store near him? If not I can see the dilemma, however while he is technically correct about a rod for "all calibers" should fit all calibers, common sense would say that a new round such as .17 hmr might fall into the category of too new. Most of theses "all caliber" rods are just .22 rods, which is the smallest caliber usually found, so anything bigger it would fit also.
"Where the choice is between only violence and cowardice, I would advise violence."
~ Mohatma Gandhi