The author used a deliberately confusing title to make the point that ChromeOS should be considered as a Linux OS rather than a distinct category. The actual stat is "Linux (excluding ChromeOS) has nearly half of the desktop OS Linux market".
There's a reasonable argument that Chrome OS is Linux--or at least more so than Android is. But it's not so much that it's "the wrong kind of Linux" according to purists as the article says but that it mostly addresses a different use case than installing Fedora or Ubuntu and therefore, IMO, it generally makes sense to treat them separately unless your point is that some form of Linux (and *nix generally) has a pretty large market share on both desktop and mobile.
I've never seen the security stuff from ChromeOS be ported to live outside of ChromeOS. When I looked at it (trying to build the inside-container agents for acustom container image), the error messages for setting it up incorrectly were.. let's charitably say hard to understand. I doubt anyone outside of ChromeOS developers understands it, really.
It's pretty intricate, e.g. giving Wayland access to virtual machines in a safe way.