I will read it too after I finish the game. But the speed runs I saw in other games used game breaking bugs or out of bounds game play to skip areas.
But it could be as simple as an how you play an NPC’s story-they would affect the main story and shorten the game to one of the many endings.
Reminds me of the old pick a path adventure books. “What do you do go right or left? I go right. A bugbear jumps out of the shadows and kills your character.” Game over you died. LOL
Having seen parts of the speed run, you start as an Origin character and do a lot of jumping (keeping this effectively spoiler free). I don’t think they’re using out of bounds, but they do “complete” the game before act 3 even starts. It’s an “Any %” run, which essentially is a run that takes you to the credits even if it’s not the end of the actual game. Apparently there is a way to trigger that state earlier in the game. Having pased that point, it makes sense what it is and why the game allows it. But it’s not something you’d likely run into on your first playthrough.
I’m sure there will be other categories added later, likely “Any % Act 3” or an any % category with other requirements, like specific boss kills or end conditions.