As written in the article, Xenix was a Version 7 UNIX, so it was not written by Microsoft and as ATT didn't licensed the name 'UNIX', Microsoft had to use another name.
I have fond memories of the much more recent Windows 2000, it was a relief from the horrors of Windows ME. Contrary to UNIXes which ran on black box hardware (DEC/SUN/Apollo, etc) Windows ran on PCs where everyone could write a driver, and it (more or less) works with the OS.
Microsoft offered an interface for drivers and tools to validate them:
https://en.wikipedia.org/wiki/Windows_Driver_Model