ChromeOS is Gentoo-based and does use the Linux kernel, but everything in the userspace has little to do with the Linux desktop besides Crostini, which is just a Debian container.
That's unlike Android, whose kernel derives itself from a heavily gutted version of the Linux kernel, redesigned to support closed source binary blob drivers provided by device manufacturers and with low level support for the Dalvik JVM. Its API has little to do with the mainstream Linux kernel.