What is going on here? Well, Nintendo itself hasn't gone into detail, but packaging for Switch 2 Edition games does note that cartridges contain both the original game and the Switch 2 upgrade.

Nintendo Switch 2 cartridges may be set to change in a certain way that could have big ramifications for the game-key card issue.

Nintendo fans have known for some time that Switch 2 is backwards compatible with Switch 1 games. But what happens when you do the reverse and stick a Switch 2 game in a Switch 1?