I refuse to believe the 20 second run is possible by any means. It has to be a splice. A very clean one at that.

the glitch roblox8192 performed is called a wall clip/zip i can tell you from a moderator and an 8-year Roblox player's perspective that it was a totally legitimate trick

if you'd like some context on how the glitch's performed, you align yourself right up against an edge of a wall, and if you turn your camera in the opposite direction then shiftlock/zoom into first person you either clip through a wall or zip right near the end of it

if you're still curious I perform multiple of these in my runs in a different game, Adventure Forward 2 https://www.speedrun.com/af2/run/z031vq8z