Well either they modified the default_mp.self or they are using a 1.11 (or earlier) .self because all dev cheats were removed since the developer.gsc wasn't compiled in the retail default_mp.self in 1.12 (and later).
*EDIT*
Yeah they are on the disk's .self. You can see the version number in the top right corner when they are in the multiplayer main menu/split screen menu.
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