TL;DR: This is about "Amazon Underground", which sounds like an attempt to undercut Google Play, and shift transactions to Amazon. Looks like it's been around since August 2015.

http://thenextweb.com/apps/2015/11/10/amazon-underground-tri...

If it's for android tablets, why not publish in the Play store?

It is on Play but it's $5 vs free on Underground -

https://play.google.com/store/apps/details?id=com.puzzleboss...