it’s the claim of it being a file system that’s throwing me. obviously nbd but maybe my mental models broken again.
File 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.
The difference between a file system and a container format is mostly a matter of perspective - indeed OSX literally uses "disk images" as their container format. Is .zip a filesystem? You probably wouldn't want to use it natively on a disk, but for a lot of purposes it's the same kind of thing.