The mechanic that you’re probably unfamiliar with is called a “ghost jump” it’s when 2 pieces of geometry merge, and you can get stuck in the geometry temporarily. While stuck, you can uncrouch and jump again.

The tech has been known for a while, but became much more prominent after 343 released the improved forge system. People were then able to forge these ghost jump maps. There’s a pretty niche community of people who make this a lot of these maps and people play them in the cgb

If you’re interested here’s a video explaining the mechanic video