ChromeOS is not Android and to get the exact definition of what they do and how they were you might need to be an expert in those systems. However from a layperson’s perspective it might be more simple and yet more blurry at the same time.
Android devices function much the same way as iPads and iPhones. It’s actually an OS (operating system), graphical user interface, some vendor required native apps and some 3rd party apps. A lot of the time the apps are nothing but portals into the browser widget API.
ChromeOS is an operating system, graphical user interface, and a browser. Everything that might need to be a native app is exposed through the APIs and is a webapp. In the last few months Google has been experimenting with native Android apps and a native Linux container.
While very similar things can be said about iPad, iPhone; Apple does not have a ChromeBook equivalent even though they have hardware in the same capability. I imagine they could but an iOS personality on a Macbook Air or mini in no time. It seems silly to me that they have not already… at least as a quick book or even as a kiosk that does not demand $1000+.
ChromeOS and it’s Android partner are pretty good together. These devices are my portals into monitoring production systems without leaking data or credentials. But then the unpredictable happens… trying to send some text messages from my Chromebook Pixel 2016 I get the error message that it’s not supported. (see it in the green text?)