True, though to Microsoft's credit, the existence of the POSIX subsystem, even as a proof-of-concept, ensured the underlying kernel design supported the development of products like Interix, just as Windows on Alpha et al. ensured NT remained reasonably portable to future platforms like ARM, unlike say OS/2 where the only non-Intel release (for PowerPC) was basically a prerelease lacking core OS features like networking.
You're mixing it up with NT's "personalities" of which OS/2 was the primary target at the time. UNIX was purely for FIPS contracts
I think they are saying that "Unlike OS/2 itself (as a competing MS and then IBM product) had less thought and design went into it as a portable system, whereas NT was designed portable ground up"