AOSP is just a subset of Google's changes made to Linux kernel.
Thanks to Project Treble, Linux on Android feels more like a pseudo micro kernel than traditional Linux.
Then it is more like Linux + grsecurity than plain Linux, as it has LinuxSE, seccomp, Fortify, hardware pointer validation (on supported devices) and a couple of other security measures enabled by default, constraining what NDK is actually allowed to do.
It has its own way of OOM killer daemon, it is compiled with clang.
Google is indeed a major Linux kernel contributor, but in the context of Android team, they only contribute a subset of their changes.