"Please bear in mind that the "official" Prometheus Facebook page is not even edited by Fox themselves. The responsibility for their Facebook and Twitter pages is outsourced to a third party company called Substance Movies.
Fox provides them with promotional material as and when it becomes available, and in the mean time they're pretty much to themselves with "tweeting" and updating their page to keep fans coming.
I wouldn't be surprised if Fox hasn't provided them with a proper cast list, so in the mean time they've had to gather information from fan sites and other places around the internet.
I've tried to get in touch with them to clarify why his name is on their list, but no answer yet. I'll keep you all updated."