Sorry for the late response. I mentioned Freedesktop in the context of the Linux desktop. Freedesktop is responsible for the desktop ecosystem typically associated with Linux, and it’s what application developers refer to when discussing Linux compatibility. Steam for ChromeOS is not referred as Steam for Linux for a reason, it’s an entirely different application. Of course, there are exceptions, such as NixOS and Alpine for example, but both of them still aim to be part of the “Linux desktop” ecosystem, whereas ChromeOS does not, and yes, it’s “Linux” under the GUI stack, but referring to ChromeOS as a Linux desktop would only confuse those less familiar with the topic or worse, mislead them.

Generally, Linux as a term refers to the Freedesktop standards, Linux kernel, and GNU userland. ChromeOS fulfills the latter two, but it lacks the Freedesktop standards, which are an essential part of the Linux platform. Therefore, it is logical to distinguish ChromeOS from standard Linux distributions since it diverges significantly from them. This differentiation has nothing to do with the Terminal, as it isn’t necessary to use it at all on most distributions. Elementary OS and Endless OS adhere to the Freedesktop standards, they are parts of the same platform as other Linux distributions.

GNU was the very first free Unix reimplementation project. Without it, maybe only excessively expensive commercial Unix systems would be available alongside Windows. Although 386BSD was also an early effort, the intense FUD campaign prevented it from being used for more serious purposes. At the time, GNU/Linux played a crucial role in competing against commercial Unix systems.