Well its hard to say what the real reason is.
The idea of bringing back the 8-bit graphics to these days, was a really good idea, but the fact that no one else can use it its ridicolous, so I don't think the graphics have anything to do (but if you use the same backgorund, or same bird, then you probably would get some copyright infrigment). All the graphics in my game made were made from sratch inspired in the idea of 8-bits
I think the problem is a combination of the play-game and the name. I saw a "swing submarines" 3 days ago, which was the same idea, but there it was a submarine instead of a copter, and there were something similar to mines instead of axes, and the game got banned too. There was also a "Swing Miley" which the copter was a Miley Cirus head, and the axes were balls (a parody of a video song of hers) and also got banned.
I dont think that I will change things in the game to upload it again, I dont want to run another risk (its gets harder and harder to get new google play developer accounts once you lost a couple)