Judging by the getting started guide[0], they thankfully haven't forked Rust or anything, this is all about windows-rs[1], a Rust library for conveniently accessing the Windows API.
So it's more like "Windows for Rust" rather than "Rust for Windows"...
It's still Rust for Windows, as in "this is what we need to make Rust an option for Windows development". Thankfully, it's not 2003 anymore when the tools involved would only run on the target OS unless written in Java or by RMS. Nobody wants to bother with the specifics of their build server environment.
They're just bad at naming - that's not what they're doing.
I hate their all caps names.
It's their Windows API SDK, same as Amazon posting about their Rust SDK for AWS.
Aws named it "A New AWS SDK for Rust – Alpha Launch".[1]