[pdonis]

404 means that there is no resource at the requested URI. But in the case you're discussing, there is a resource at the requested URI; it's just a resource that says there's no user there, instead of a resource that gives data for a user.

In other words, using 404 the way you describe conflates two different things: an invalid user URI (maybe the range of possible user IDs is restricted, or you typed in the URI wrong) and a valid user URI that just doesn't have a user there at the time you made your request. But you probably don't want those two things to be conflated; you want them to be distinguished. That's the article's point.