It all comes down to what your using as your definition of “Unix”. Unix is (or at least was) a trademarked term, and not a generic description. Minix, Coherent, and other similar systems were not, and could not be, “Unix” despite offering similar services, since they weren’t able to use the trademarked term.
You can’t define a Unix by its kernel. You can’t define a Unix by it’s tool set. If you define a Unix by its process architecture, how it uses devices, it’s reliance on ubiquitous block and character devices. It’s availability of services such as pipes and fork, its virtual memory system, by it’s user land development model, then lots of systems are more Unix than not (including things like Minix, and Coherent).
Is Unix little more than fork, open, close, read, write, ioctl, select, and sbrk?
If you simply use the Wikipedia definition of Unix:
Unix (trademarked as UNIX ) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix…
Then, Minix, Coherent, and Linux are not Unix. Because it did not derive from the original AT&T Unix (As SCO painfully found out in its disastrous lawsuit).
But if you told someone that Linux is not Unix, they’d either laugh at you or tell you that you’re splitting the finest of hairs. Or that you’re a lawyer.
For billions of people, Linux IS Unix.
Android is based on the Linux kernel and user land, and is as Unix as any other Linux based machine.
So, while the term UNIX has actual weight, it’s trademarked, and the trademark means something, in popular culture, Unix is essentially a generic term that means “Linux and all those other guys”.