Kevin C. Tofel is a technology writer who focuses on Chromebooks. He recently mentioned in an article that ChromeOS is now more like a Linux distribution with the Google desktop environment .
He said that although not everyone knows it, ChromeOS is actually a Linux distribution. This fact is effectively hidden. His take on this: For mainstream consumers, Linux can be a scary word . But there's no denying that ChromeOS is Linux - it uses the Linux kernel but is hidden by a graphical user interface (aka desktop environment) .
He explained that when you install Linux, you choose a distribution. It could be Arch, Fedora, Debian, Ubuntu. He himself uses Pop OS! - which contains a Linux kernel as well as software and modifications for that particular distribution. You can think of the kernel as the lowest level of software. It helps other software interact with hardware to form a coherent system. That's why you can browse files through the app or the terminal.
However, this is only part of the system. The other part is how you interact with it. Some people prefer to use the terminal and command line to do everything, and this approach involves a relatively steep learning curve. So there are graphical desktop environments to help solve this problem. These environments will visually display clickable folders, or have an application launcher menu, etc.
Although most Linux distributions come with a default desktop environment, users can install and choose from many other environments. But you can't do that on ChromeOS, which is why he said ChromeOS uses Google's desktop environment .
So going back to ChromeOS and the underlying system software, it's Linux. Google uses a customized version of Linux you've never seen before .
Kevin C. Tofel further explained that when you open Linux on ChromeOS, you will see a terminal and Debian Linux container running in a virtual machine. This is why you can run Linux apps on ChromeOS.