"Unix kernel is hugely popular: think of the millions of Android devices."
You probably meant Linux, not Unix. Unix is an entire class of operating systems, not a kernel.
Nitpicking aside, the huge problem here is that popularity means nothing if the user is not aware of what he/she is using, so I would rephrase that as "the Linux kernel is hugely widespread ...".
There is still a big problem though: Android is mostly closed, at least all vital device drivers are, so that you have no chances to build a working non Android environment on newer devices or patch old ones, move an installation from a device to a different one etc. Having a Linux kernel does not help in this context since all benefits the FOSS community infused into the system were stripped away.
I would dare to say that telling people that Android contains a Linux kernel is even dangerous to the Linux image.
You probably meant Linux, not Unix. Unix is an entire class of operating systems, not a kernel. Nitpicking aside, the huge problem here is that popularity means nothing if the user is not aware of what he/she is using, so I would rephrase that as "the Linux kernel is hugely widespread ...". There is still a big problem though: Android is mostly closed, at least all vital device drivers are, so that you have no chances to build a working non Android environment on newer devices or patch old ones, move an installation from a device to a different one etc. Having a Linux kernel does not help in this context since all benefits the FOSS community infused into the system were stripped away. I would dare to say that telling people that Android contains a Linux kernel is even dangerous to the Linux image.