Icon packs are in a tricky legal gray area. Almost all of them (if not all) contain trademarked images legally owned by the original developers, and to make matters worse, many icon packs are paid. One developer recently submitted a new icon pack to the Play Store, only to have it rejected for "content owned by a third party."
The developer in question is Saurabh Gupta, who attempted to submit 'Android O Icon Pack' a few days ago. It was first rejected for using Android in the name, and after it was submitted under another name, it was once again rejected. The reason provided was, "Remove any content owned by a third party from your app."
It's very possible that this is just an isolated incident, caused by a stricter-than-normal reviewer. But it could also indicate that Google is starting to crack down on trademarked icons and logos in icon packs - only time will tell.
- Saurabh Gupta (Google+)