The guy found his way into some then-unused maps through the debug room, probably. The maps in question were fully added into the game in ver 0.19 as the vomitgirl area (named after the folder holding said maps). From version 0.193 the maps MAP0280 (pic) and MAP0285 have been in the game in a similar fashion where they can only be accessed via debug or by opening it up with RPGmaker.
Funny detail is how lol_rust really likes putting holes in white hands now. It's the same as the character design for Mimimi, the playable character of Aruma Ketera, who is also lol_rust's vtuber avatar.