Back then I had assumed that it was just someone at 343 playing with the helmets on their internal builds, but now that people have brought up the "Armory Complete?" bit for when you get 100% and inheritor, I'm not sure. The main reason I didn't believe it was because all the armor models have been extracted from the game, but the tag structure in Reach was completely scrambled, so that makes me think they were just looking for changes in the calls to the armor idents and used those to identify and extract them, leaving the possibility of unidentified pieces.
Don't take anything I said seriously, it's just speculation.
Would anyone like to do a campaign run through just looking for stuff? I've yet to do much shenanigans in the Reach campaign and have just sat back as people have found everything. Ghal? Hitmon?