One big problem with that is that my photos app will show all of the assets in it, so yeah I can't hide the game and so it's better if it's in an apk form
Adding a file named ".nomedia" into the root directory of the game will tell your Android phone not to look in that folder for media files, which should prevent your photos app from displaying them. I use that method on my devices
Most (decent) photo apps also have a setting to exclude specific folders, so you can try that as well.