Did you people already have a credit card on file with them? Because I didn't and it definitely asked for one, then the game went through fine, and I promptly went into the settings and deleted the card from them.
Alright, I'll explain the whole thing for you and other people wondering about whether or not a credit card is needed to get the game.
If you went ahead and tried to get a download code from Xbox.com and you don't have a credit card on file with them, it will prompt you to 'Add a Credit Card' despite it being a free game. However, (and this is important) if you go on your Xbox 360 and searched for 'Witcher 2' on the dashboard, you can download the game
without a credit card there no problem (no download code is given, you simply just get the game).
If you have an Xbox One and don't have a Xbox 360, then the only way to get the game on your Xbox One is to give them your credit card on Xbox.com, take download code, and input it on your Xbox One. Delete the credit card on file if you wish.
Go to the Xbox 360 dashboard, search for the 'Witcher 2', and download the game. After it is finished downloading, go to your Xbox One dashboard, search for the 'Witcher 2', and press 'install'. No credit card used throughout this entire process.
Note: If you think you can go straight ahead to the Xbox One dashboard and download/install the game without first downloading it on your Xbox 360, you are mistaken. It will show the button 'Bundle Only" with no option to download/install. Only when you download it first on your Xbox 360, and then go back and search for it on your Xbox One will an 'install' button appear magically.
Another note: Obviously, make sure that you are signing into the same gamer profile on your Xbox 360 and Xbox One as you are doing this. The whole purpose of downloading first on the Xbox 360 is to allow it to show on your profile, and enable downloading of the same game straight to the Xbox One. You can delete the game now on your Xbox 360 if you don't want it there.
Hope this helps people and it puts an end to any more credit card questions.