How does Google Play rank games?

I released a mobile game last December and yesterday I found out it's #23 Top Paid Arcade Game
https://play.google.com/store/apps/category/GAME_ARCADE/collection/topselling_paid

The thing is, the game has 10-50 installs and 7 reviews(4.9 avg) and its ranked better than a Sonic game, a Star Wars game, a game by Rovio and a game by Vlambeer. Those games have 10000 more sales than mine and lots of reviews and I really suck at marketing so if this is not some sort of glitch I'd really like to know whatever it was that it's working.

Google about how Google Play ranks games returns lots of blogs and articles with very different opinions, so I thought maybe someone here has some experience with Google Play and can tell me whats going on.