CA does call themselves The Creative Assembly.
Check out their website and official logo.

Also, they used Activision in the sequence, which could cause legal troubles if this was indeed a hoax.

I think it was a leak that gave this info away. This intro/teaser movie is probably what was shown to PC Gamer and prompted the article on the next TW. I think that as a result of this, the CA staff is being ordered to keep their mouths shut until official word gets out.