That was back when there was "real" UNIX around, as well as a number of clones, including Microsofts own Xenix (maybe they had offloaded that to SCO by then). So UN*X was one way to indicate that it meant UNIX-like OSes.

It is a generic way to refer to unix and unix-like systems. It is still in use today, e.g. to indicate Linux as part of the set. For this document most likely it refers to Xenix (MS's unix).

IIRC Microsoft's internal email still ran on Xenix at the time (until Exchange betas got good enough for internal use c. 1995?), so perhaps more trademarks than some sort of absolute hatred of Unix. Also note that one of the two APIs that NT OS/2 was initially going to support was POSIX, albeit perhaps more because the US government wanted that than a true love of UNIX. Although the design rationale document (ntdesrtl) does lament that existing POSIX test suites tend to also test "...UNIX folklore that happens to be permissible under an interpretation of the POSIX spec".

I think trademark, I remember Bill Gates referring to Windows NT as "a better UNIX than UNIX".