Update: The Third Floor, whose watermark appears lower right, is a production company listing Blizzard as a client. StarCraft II: Wings of Liberty cinematics appear in their publicity reel.
read that in the OP link.
anyway, it feels legit to me. mostly because of the voice acting. the characters sound pretty much the same as they did in Wings of Liberty. won't change a thing about my curiosity to find out what happens with the zerg, or Kerrigan. her mutation to the queen of blades (again) could easily be explained. her hair didn't change through the use of the xel'naga artifact and her... mutation could kick in again soon after the effects of the artifact passed. apparently she's in a less destructive mood and probably works with Raynor that she trusts again.