Why on earth would it be a tube?
That gives no semblance of shape for the human head whatsoever.
I looked at your vid where it shows it considerably more clearly, and while yes, there's somewhat defined texturework to it, I would seriously doubt that it's the real face of the cheif.
One thing that bugs me is by the looks all the detailing of the nose, forehead, etc is simply drawn on with heavy lining to give it better definition and there is no apparent real detail work done to the eyes, so we're either looking at a very early stylizing of cheif's face, or it's placeholder.
Honestly it could be either at this point, but if they really do plan to show cheif's face in Halo 3, it's got a lot of work needed on it yet.