Due to my limited access to the internet, I'll write it down here, because too much people asking for it. And by the way, I really hates that leakers.
The app itself called RootCloack and was available to download in Xposed framework.
To make things undetectable, just add the app into the list within the first options, while the second is to make ANY keywords used by the game dev to search or detect your hack tools, e.g. Game Guardian -> Game, Guardian, Game Guardian, GG, and more.
Goodluck.
Please take a note that you may try to full uninstall the game and clear ANY files related to it which is left behind.