linuxmemes

I think they use some very old and heavily modified version of the Linux kernel, so it's not the same Linux kernel we use on desktop. Then each phone manufacturer adds custom patches on top to support their hardware. GNU/Linux phones also require a custom kernel, but the community is working on upstreaming those patches, so that they can run mainline kernel some day (PinePhone Pro and Librem 5 probably already can now, but some stuff might not work).

Yeah, using the name Linux for both the kernel and the operating system makes no sense and it's super confusing. When people say Linux when talking about the operating system, they almost always mean GNU/Linux (like Linux Mint, Arch Linux, etc). But then there is Alpine Linux, which isn't GNU/Linux and that makes things even more confusing. If I didn't know what Alpine Linux or Arch Linux was (and had no knowledge of distro names), based on their name I would assume they are some kind of fork of the Linux kernel. Arch Linux should have really been called Arch GNU/Linux and Alpine Linux should have just been called Alpine OS.