Not everything from Android is in the mainline kernels. There are still a few bits that are Android specific that would need to be reworked to even be accepted into staging.

There has been a lot of great ARM work lately in mainline too but there are still quite a few drivers missing that you can't even get docs for (even with signing NDAs) so the drivers for mainline get written based on the BSP-ish kernel drivers which aren't always written the best.

He never said it did. He said that they can use Android kernel and drivers. That doesn't mean it's using Android's java environment, just the kernel and drivers beneath it.