If you dl the map and check its description, says it was made for the 2011 MapCore Cube competition, by Sam Combs.

“The only rule for the competition was that the playable area of the level had to fit entirely within 1024 by 1024 by 1024 unit cube. For scale, the player in HL2:DM is about 64 units tall.”

He’s interested in polishing and releasing it if you guys see potential.