I just booted up the game and started playing for a bit and then I realised that I didn't even have the disc in the console. I took it out last night to play another game.
I wasn't aware this could happen without buying the digital download.
Can't say for Xbox but I know there's a trick on PS4 that allows you to "delete" a game's file from your console and then download the game from your gaming Library that allows it to function as a digital download.
Not helpful for you but maybe Xbox has some similar trick to it that would allow this to occur.