alt Hacker NewsFile system is the wrong word. What they should have used is file format.
It is not wrong that you can have a file (bits and bytes encoded in the shape described by a file format) on some remote point. If you have an index of those files where you can programmatically choose between multiple files that could even pass as a crude "file system". But I doubt this is what they meant to refer to.
It is likelier they wrongly assumed a file system is the system in which a file is organized, where in fact they meant file format.
I think they were going for a reasonable analogy, especially when a stream is saved to disk to have its contents extracted: each channel contained in the stream can then be thought of as a separate file, not unlike files in a zipped directory.