do you mean in the same way that debian/fedora/gentoo are also not linux? I'm not being sarcastic, i'm just claryfing.
Debian/Fedora/Gentoo are all distributions of the same OS (GNU/Linux). A distribution is just a collection of packages, basically. The only difference is, is their philosophy, package manager, and maybe a few apps. Userland tools, xorg, shells, utilities, etc are mostly (if not, all) the same.
Think of "GNU/Linux" as a tree trunk, while distributions are the many many branches sprouted from it. Or an ice cream cone, with various flavors of ice cream stacked on top of it.
So with Android (semantically speaking), it's really Android/Linux (w/o the PR n shit).