Android is definitely not a GNU based distro but whether it is considered a ‘pure’ Linux distro as per se is still subject to debate, while this may have sparked a lot of controversy among Linux evangelists the fact remains that Android still runs on the Linux kernel. – A device-specific kernel that was once a heavily forked inbreed version of mainline Linux until Google decided to take the matters into their own hands.
You’d probably notice that your Android device runs atop a certain version of Linux Kernel, for most Jelly Bean users out there the version clocks in at 3.4 while ICS-based handsets usually employ Kernel 3.0.y and the late Gingerbread packed the aging 2.6. With each release Android is packing a newer kernel, a mostly unaltered kernel that otherwise bears a striking resemblance to its mainline cousin. Over the years upstream Android patches (e.g wakelocks) and additions have made it to mainline Linux and most mobile SoC sources & blobs have been merged into the main kernel source.
Google on its side is still playing around with the latest stable Linux Kernel judging from their experimental 3.10 public repo. The bits aren’t quite ready for compilation but that gives us a glimpse that future versions of Android could embrace a significantly newer kernel version. We cannot ascertain if Kernel 3.10 will make its way into the upcoming version of Android (KLP) but the fact that Kernel 3.10 is the 10th longterm release could indicate that Google might want to adopt it sooner than expected.
Let’s not forget that the two last flavors of Jelly Bean (i.e 4.2 & 4.3) make use of the 9th longterm Kernel release (Kernel 3.