It's implimented as a magic filename? Not a virtual or real file that actually appears in a filesystem? You don't have to do something like mount a virtual fs that maps to your host windows fs like a bind mount or nfs mount, and also add that fs to PATH?
The entire point of WSL is seamless integration. Windows drives are automatically mounted as /mnt/c, the Windows PATH is added to the Linux one, and it can run Windows .exe files and communicate with their standard I/O.
If so, that sounds terrible, and very Microsoft.