Maybe he is aiming at the fact that the level itself consists of geometry within an area of almost nothing besides a background color. Maybe you can add geometry that's just too far away to jump to or slide on? I'm thinking about rocks and cliffs, the interior of a butcher's room or something, I don't know, if the geometry interfers with the camera then adding it is not a solution, maybe the idea of adding blood rain alone will already solve this emptyness??

Cheers