Nah, looks to be just an idiot going around claiming he knows that K3 is being made. Just wait until LA says "Yes" or "No."
Really, they're following Bungie. Bungie, in Halo 2, made a huge cliffhanger ending, and then said, "Hey, we're not doing the Halo series anymore. We're busy working...working on Phoenix! Yah!" They denied all rumors that they were doing Halo 3 and worked very heavily on "Phoenix".
And then, come E3, Bungie said, "You know about us telling you repeatly that Halo 3 is just a rumor, and that we are not going to make it? We...er...lied. Sorry." And everyone cheered at the trailer.
SWKOTOR2 has a cliffhanger ending. Obisidan says that they are not doing K2...See the resemblence?