You have no clue how the engine is designed, only what is being displayed
You set the drawing distance(which will still apply if you fall through)
In this case it would only be rendering it since your client if out of bounds.
imagine most games a god-mode where you can fly out of tge map

Theres also a mapping technique that lets you do 3d sky boxes small off map render, and appear much bigger around(essentially what those areas are, blocked off sections)