Total Amnesia is talking the science in the fiction and applying it to the spirit, not just the physical universe. Its entire basis is that you ARE a spirit. So why aren’t you acting like one? Why can’t you simply fly across the universe and blow up a star?
“Oh no no no!” You say. “You can’t ‘fly’ without a spaceship you’d freeze! You can’t blow up a star, you’d get vaporized! And what if there’s a populated planet nearby. You’d kill them all! Furthermore, you can’t see without eyeballs and optic nerves or hear without Semicircular Canals and Tympanic membranes and you certainly can’t think without a brain! Right?”
Wrong.
In this story, flying across the universe is the most natural thing a spirit does. Agreeing with all the material constraints is the most un-natural thing you do! How did you get into this condition? That’s the adventure of Total Amnesia.