It was Rust/WinRT, then they added support for other kinds of Windows APIs alongside the WinRT support. Someone probably thought Rust/Windows looked weird, so, Rust for Windows.

Rust/WinRT was called that because it was patterned after C++/WinRT, which was called that because it was a replacement for or alternative to C++/CX, which was called that because it was an analog to C++/CLI. C++/CX and C++/CLI are language extensions/forks, while C++/WinRT and Rust/WinRT are just libraries (and tools).

(I always thought C++/WinRT was a bad choice of name for this reason)