Why are you so upset? I think you imagine this the wrong way.
This is how it looks inside git. Git is a tool that lets you organize your code versions and make collaboration easier. I could imagine him having at least one branch for stable releases, one for playstore beta testers and one he's working on. If you write your code "right", you are able to take pieces out and move them around.
If i understand correctly, he just took one fairly stable feature and attached it to his older code. For testing. This could be beneficial for the project as he can