No, I think you got me wrong. No offence but, like many, you do not seem to understand what "Linux" really is. Do not worry, you are not alone in this. Especially people with many years of experience in running Linux on x86/64 servers or workstations often make wrong assumptions when it comes to embedded systems, like phones.
Android does use a real Linux kernel, and thus is a true Linux system. You can grab its kernel source from kernel.org, configure it to you liking and create your own custom ROMs based on it. The only limitation is that you practically can only run the single major ke