What is being depicted w.r.t. AoA in this video?
There are several colored lines.  Which one are you asking about?  I'm assuming you are referring to the (cyan?) and red lines in the upper right inset.



The cyan line shows the current direction of the airflow.  When compared with the orientation of the airplane can show the angle of attack.  At this time, the relative wind is coming at a very steep angle to the airplane and the wing is stalled.

Another way to see it is that reversing this arrow shows the direction the airplane is moving through the air.  In a no-wind situation, this would also be the direction the plane is moving with respect to the ground.  

The red line is at a constant angle with respect to the airplane and shows how low the airflow can go without causing a warning.  As it is below this line, the stall warning has sounded.