I see them as 2 slightly different declinations of the same use case, which is provable ownership, which is what NFT basically is. You can prove ownership of a unique item, like a painting, or a sculpture, but you can also prove ownership of a specific copyable item, like a book, in which case your ownership will be linked to an immutable version of that item.

You can prove that you own a specific versin of a book, not modified, maybe a princeps, limited edition, etc... Value may come from the fact that content is provably unmodified. Back in the day, people will pass on books from generation to generation, in some cases way before the print press was invented (religious teachings, for instance, or guild rules).