The game normally doesn't have War Chieftains and flood in the same area, so there's no proper form linked to an infected WC. Most likely it's a quick infection prototype that was left in. Instead of instantly becoming totally floody, freshly infected hosts would be almost the same as they used to be. The whole takeover would happen over time. Bungie then scrapped the idea for some reason, probably recognition issues, but one model was forgotten in. [Edited on 02.04.2010 4:55 PM PST]