Don’t know if you ended up watching it, but effectively they’re able to randomly execute code during the loading screen using a bug caused by audio generation vs controller polling. So by using TAS tools they can spam the controller to cause an audio bug that let’s them jump to executing code from Ram that they are able to manipulate using controller inputs.

TLDR: Using a bug in the audio processing, they can use controller inputs to write arbitrary code that jumps them to the end of the game.