Originally, ChromeOS was the Chrome browser with just enough code to boot to and take care of other essential OS functions. Like, the system settings and browser settings were practically merged.

The author is alluding to more recent efforts to untangle and separate ChromeOS from the Chrome browser. I believe the goal is for the Chrome browser on ChromeOS to be essentially the same as other Linux browser builds.

So these days ChromeOS is structured more like other Linux distros, with a huge difference being how locked down it is.

[Insert GNU/Linux interjection copypasta]

There is a common understanding of what a Linux Desktop look like.

Whether you run Gnome, KDE or XFCE, you can install the same software and when you open a terminal you can do more or less the same thing.

ChromeOS however have a completely different user space. A bit like Android, yes it uses the Linux kernel but it's not what people think about when they talk about a Linux Desktop.