Android as well. These are operating systems distributing Linux Kernel, therefore they are Linux distributions. Nothing more, nothing less. From there, it depends what the use case is to classify an operating system. Is it a Desktop system? A smartphone system? Or specifically made for gaming? For IOT devices or for servers or for supercomputers? Does it use GNU tools? Where is the line when you stop saying it is Linux based operating system?
Linux is Linux. ChromeOS is distributing the Linux Kernel. Even if an operating system wouldn't use the GNU tools and if you could not run the application that runs on your Desktop PC, does not mean it wouldn't be Linux. I don't care how people categorize it or arbitrary ignore Linux based systems.