Can't help but think this was just a marketing error. Had they called the OS something like SurfaceOS instead of WinRT, perhaps the expectation would have been something more accepted, akin to iOS and MacOS.
Sadly they keep making that mistake by pushing for "Windows" for their mobile OS and as you mentioned, ARM OS as well. They really should not try to push "Windows" where it's not really wanted, but instead re-brand for other platforms, and allow it to all come together.