It is currently unknown why Bungie put it there, though it is possible that Bungie originally planned on having John-117 play a bigger role in the Halo: Reach campaign, instead of only giving him a cameo appearance (at the end of the level The Pillar of Autumn).
After playing the level Lone Wolf, go to Theater mode and pause the camera a few seconds into the level. Then, rewind to the very beginning of the clip and detach the camera. You should now see a large segment of the Aszod yards, which form the background in the actual level.
Zoom over to the shipyards, and in between the two yellow cranes is a tiny Master Chief model.