It runs a linux kernel, which makes it a Linux based OS. It probably integrates a lot of linux stuff too, and it of course comes with virtualization support (leveraging the support for this in linux) to run proper linux applications and development tools, etc.
It's big enough to be worth counting separately though. Interesting that regular linux now has twice the market share of Chrome OS.
It still isn't GNU/Linux, and if ChromeOS virtualization counts as Linux, so does WSL, as the technical approach to run GNU/Linux inside its own VM is quite similar in both OSes.
Normal ChromeOS users only have a browser based userspace.
Semantics. GNU/Linux is a subset of linuxes. Chrome OS runs a linux kernel, includes lots of libraries and other things from linux, which, like it or not, makes it another (and pretty significant) subset of linux. Which is why it is counted separately.
Do you think normies are using GNU software on Linux desktops? Or do you think they use software like Dolphin, Nautilus, Steam, Chrome, Firefox, Plasma, etc. A desktop environment doesn't expose GNU/Linux. It requires people to open a terminal to get to it. ChromeOS has its own terminal that uses bash and has its own set of coreutils for people to use.
It's big enough to be worth counting separately though. Interesting that regular linux now has twice the market share of Chrome OS.