A distinction without a difference. The point of this subthread is that the term Linux is overloaded to mean two things: a kernel and also an OS that has certain assumptions (usually glibc and some unix userspace stuff).
The point being that “Linux Desktop” means something more than “runs the Linux kernel”.
Which is exactly why people here talk about "Linux Desktop". Linux is a kernel, Linux Desktop is some flavour of a full OS made to run on a PC, as opposed to e.g. embedded Linux or a Linux server.
I think that's pretty pedantic. When most people here say 'Linux Desktop', they mean the Linux kernel, GNU(-ish) userland, Wayland/X11, and some desktop like GNOME, KDE or Mate.
Though, I guess outside tech circles, people will just talk about Linux as the whole desktop OS. E.g. our municipality was promoting installing a Linux distribution to save Windows laptops after the Windows 10 apocalypse, and they just call it Linux.
Even Wikipedia says: Linux (/ˈlɪnʊks/ LIN-uuks[15]) is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds.
But with respect to "Linux on the Desktop" in the context of marketshare, the interest is in seeing how far Linux has gone, not how far software running on Linux has gone.
The only reason "ChromeOS" isn't considered Linux in this dataset is because Chrome has a flag that removes Linux from the user-agent on certain systems. If we were talking about Linux on the desktop casually, or were compiling a dataset through some other means where the kernel is a known quantity, we'd most certainly include said systems.
Linux is a kernel.