The point is, "resource" is an abstraction that servers may implement as they wish. The only requirements, per HTTP, is that (1) it's something that can be identified with a URI (satisfied in this case), and (2) it has information associated with it that can be retrieved and/or managed via the HTTP protocol (satisfied in this case).
We might imagine that the set of resources should be finite, or strictly mapped to extant data records in our system – but these are not requirements.