There of course can be substantive differences between two substances, in which case it's certainly justifiable to affix descriptors to the two materials so that they can be told apart. If one of them is better suited for a particular use than the other, it's perfectly sensible to communicate that to possible purchasers.
It however has been very common for many years for general material suppliers to sell their products in a medical version for which medical-use-appropriate documentation exists and (sometimes) for which medical-use-required testing has been done, and an industrial version that is chemically and physically identical and comes from the same production process but is not so documented and tested. This is a straightforward way to (try to) apportion the extra costs of such documentation and testing only to those customers who need those added services, while keeping the product version for which such services are not needed at a more competitive pricepoint.
This, over time, has morphed in material marketing into a common practice of just offering a "medical grade" at a higher price, with no additional services provided on the basis that the buyer is expected to do the materials qualification and documentation.
In my experience, far more often than not, "medical grade" has no substantial meaning other than that the medical-device-maker purchaser is thought to be willing to pay more.
Of course, this has to be applied intelligently and knowledgably.