A kernel is the lowest part of an operating system. Android is named after the OS which runs with the Linux kernel.
The OS that we actually use, running with the Linux kernel, is GNU. When RMS, who started the GNU project with the $1M he got as a McAthur Genius grant, the first thing he did was make the first FOSS C compiler, gcc. When Dennis Ritchie wanted to create UNIX, he wrote the first C compiler.
The OS was named UNIX, not after the kernel. RMS is entitled to want the OS to be called GNU/Linux; our beloved OS wouldn't exist without the project RMS started. LT himself (understandingly, considering what he has done himself, and human nature) calls the OS Linux himself.
Both men are completely set in their ways, and it is notable Linus, in that famous first post, mentioned that it worked with GCC, so the kernel was built with GNU in mind. The GNU "Hurd" kernel is still unfinished, while the Linux kernel has had thousands of contributors.
And the Roku, Amazon Fire, set top boxes, and a plethora of other devices are built on the Linux kernel, but the kernel is NOT an operating system. It's what makes an operating system work.
So, we can call it Linux, or GNU/Linux. Stallman gets less credit than he deserves, and he's no more irascible than Linus