Doesn't seem like it: http://www.shikadi.net/moddingwiki/Commander_Keen_1-3_Level_...

http://www.shikadi.net/moddingwiki/RLEW_compression

Looking at a hexdump of the Keen1 file matches those specs. Keen 4 uses another, more complicated kind of compression, too: http://www.shikadi.net/moddingwiki/Carmack_compression

They might be thinking of earlier Id software games. Some of those weren't compressed, and you could at least edit them with a hex editor pretty easily.