Windows is implementing the Linux system call interface. So it's valid to include Linux in the overall name, since it's running binaries designed and targeted at Linux's own APIs.

GNU/kWindows might also refer to Cygwin or gnuwin32, which are ports of GNU software to other operating systems.

And people might run zsh and busybox on top of the Linux subsystem, and eliminate GNU entirely.

But overall, I'm just tired and sick of the GNU project attempting to correct people on technical matters like this. I remember having a very technical conversation talking about the Linux kernel and its APIs, when rms came in and "corrected" us to tell us that the proper name of the OS is GNU/Linux. It's just rude and unwarranted at this point.