I am not sure about the answers here... That "bundle", what is it? Is it a game on a disc (you mention a seal)? They specify the Series X on it because the S doesn't have a disc reader, making the game disc "compatible" with the X only.

The game itself is of course compatible with the Xbox S, but you need a digital code to get it on there.

The series S is digital only and has a small hard drive, otherwise it runs (99.9%) of all the xbox next gen games. I have one, I love it, but be prepared to manage the hard-drive space closely.

Edit: Pro-tip: If you got a disc, returns it and get a few months of GamePass for XBox. Your son will have access to hundreds of games, including Fifa 22.