Perhaps someone who's more versed in Apple tech can weigh in, but my limited understanding is that tvOS' users are mostly an illusion - the current user is just a flag exposed to running apps, and each app decides on its own what (if anything) they do with that information. There's no system-level separation of data or permissions for different users.

(In my experience, most non-Apple apps just seem to ignore user profiles on the Apple TV, and either behave as single-user apps, or have their own totally unrelated user profiles.)