The speedrun is easily explained with just "RNG." Every drop in the game is random, and varies depending on the material, ex. stone and trees drop anywhere from 2-4 of their resource, while zombies drop anywhere from 0-2 of theirs. The stamina bar is also quite important, as you have to wait for it to fill before doing things like mining gem ore. It's a pretty easy run to learn, but mastering it and grinding it is another story.

If RNG is something you hate, then try "Dream%," which uses a version of the game with most drops altered to be max every time. Zombie spawns and seeds are still random, but it's certainly less RNG. The route doesn't change, either.