Even though the [character][1] appears in the credits as "Young Man", he talks knowingly to Ezio, takes his hand, tells him "Courage, Ezio". So he clearly knew who he was talking to. He's the only unnamed character in the 20 minute video. 

I just can't shake the feeling that it's not such a random encounter. So, who could he be?

  [1]: http://images.wikia.com/assassinscreed/images/a/a1/EzioYoungMan.png