In fact, they never say it’s not Linux. The summary would be more like: “ChromeOS should be counted among desktop Linux, because it has the same basis as any other GNU/Linux distribution, unlike Android. Here are the dumb reasons I think people would argue against this.”
As far as I know, ChromeOS is also GNU/Linux (It uses full glibc, includes gnu utils and bash), so not so much.
They mention this in the article.
In fact, they never say it’s not Linux. The summary would be more like: “ChromeOS should be counted among desktop Linux, because it has the same basis as any other GNU/Linux distribution, unlike Android. Here are the dumb reasons I think people would argue against this.”