Der Flatulator
Member
Which, what it boils down to, is mostly within the campaign. I'm sure they oversaw the majority of everything in Halo 4, however they just weren't the ones to implement it.
Oh they implemented a fair bit of it. There's only so much you can take from engines, middle-ware, prior games and contractors. They did use a lot of middle-ware and APIs, but that's understandable, considering the scope of the project.