User content beyond specific books?

Sometimes when I go to delete a user who has no books associated with their account, I get the message that I should attribute their content to someone else. But if they have not roles in any book, what content would there be?

@milesli3 it’s true, that message is a holdover from WordPress and is somewhat confusing. In this scenario, they would have no content; that message can be disregarded while proceeding with deleting the user.