Android studio 3.0 is responsible for this file. You don’t need to worry about the output.json file.
Let me explain this to you:
For older versions, what Android Studio did was generate a signed APK and put it in the “output” folder. Even If you had multiple flavour dimensions for your APK, all of them could be located at the same directory, which was the output folder. From the latest release of Android Studio 3.0 (canary and stable), they have organized this file structure. For every flavour dimension, whenever you sign an APK, it will have a separate folder with a corresponding output.json file in it. This file is actually nothing but a description of the source APK. As you can see, the file you shared here is describing the released APK.