you are talking about someone else. I am talking about the guy with the list at the beginning. He is Nord, not Imperial yet he works for the Imperials. It makes me wonder if he is Esbern and feels bad for your situation and catches up to you later.
No, I'm pretty sure that is still Hadvaar. you start following him once you exit the burning inn which you landed in from the fort. You can see him most clearly, at 11:58 into the video; when the player runs through the space between the house and the wall, a dragon lands right in front of him and he turns around to see Hadvaar. You follow Hadvaar until him and Ralof stand off at the entrance to the keep - "I hope that dragon takes you all to Sovngarde". Then you get the option to follow Hadvaar or Ralof into different entrances of the keep. Personally, I think Esbern will find you later in Whiterun.
Edit: Basically, if you go to 11:58, you will see that the person who you are following, whose name is Hadvaar, is the nice Nord with the list.