Congratulations, you're the First person to receive an update beyond 5.0.1 for the Nexus 9
I would venture a guess that it might have to do with the coming 5.1.1 update (maybe something in 5.0.2 is needed before the jump??).
That's just speculation though...
Interesting none the less
I got 5.0.2 on my Nexus 9 about an hour ago. It's still stuck on the boot screen. Surely Google should have fixed this problem when it was reported on the Nexus 7 over a month ago before releasing it for the Nexus 9? What's happened to common sense, let alone quality control?
Very disappointed with Google at the moment.
Seems smooth, but I don't use mine enough to really notice if there was an improvement. Upper rear corner was pretty warm after it updated and I used it for a little while. Cooled down now.