It doesn't have to. A text editor could easily present its current buffer and other properties in the form of a file system interface. See e.g. how Linux allows

It doesn't have to. A text editor could easily present its current buffer and other properties in the form of a file system interface. See e.g. how Linux allows to interact with processes through the /proc file system. There's no reason to restrict this to kernel objects. FUSE also allows user processes to implement a file system but it's clunky as it breaks a lot of old assumptions. See the Plan 9 operating system for an earlier clean implementation of this concept, including programmatic interaction with your text editor through file APIs.