They never said anything about AC3.
What he is trying to say is that:
Assassin's Creed I is about Altair
Assassin's Creed II ( Including Brotherhood and Revelation ) is of Ezio's journey, so that's like one complete whole chapter. Think of Brotherhood and Revelation as an expansion to the storyline of Ezio.
Thus predicting that Assassin's Creed III would take place in a new location with a different protagonist which obviously could be Desmond as stated by Petar.
Correct me If I'm wrong cause I'm not that good at explaining :<