If you watch it all the way to the end you DO see that it was produced by Fincantieri. I really don't believe it is any kind of a fake.
My gut feeling is that it is a promotional "idea" video that Fincantieri made for Carnival's amusement just to spur them with new ideas. As I said, Carnival has not truly innovated their shipbuilding in years, not like Royal Caribbean has. Fincantieri would love it if they could come up with an all new design for them.
Imagine how much more profit there is in making something like that from scratch than there is in being asked to "add a spa-deck to the old Conquest design".
Nothing wrong with Carnival - they are extremely astute business people. It is just that they don't sell the "wow" as much as other companies do.