I don't think so. If so, it would have been a low key announcement. It was probably an announcement on a developed game's ship date (hence the publisher problem, if you look at the note they give).
It was another Halo. A Microsoft rep confirmed that the announcement was going to be about a yet unanounced title in the Halo universe. NOT Halo Wars, because that is not being made by Bungie, but by Ensemble Studios.
It is not a Halo 4. It will not be a sequel of Halo 3, but a different game set in the Halo universe. It could be a side story, a prequel, or something else. All the details I have heard suggest it is some sort of Halo squad-based shooter.
with halo they can do a lot, if you read the books you will find that there is a lot of stuff that goes on a lot of squad based HIGHLY tactile shooting (more then GRAW or RSV) they could make a lot off good games that are about other teams like the ones from the Spartan II program or the Spartan III program.