The map was constructed out of several maps from HL2 and Episode 1 in order for me to get a long enough road for the singer to walk down.

For every NPC on the map, they have an associated ai_relationship entity telling them to ignore the singer and !player (the cameraman). Luckily this doesn't usually matter as the camera moves separately to the player. There's only a few scripted sequences in this, primarily the animations for knocking down the door and rappelling down the building. The rest of the NPC's are controlled by the ai and are told where to go by using ai_scripted_schedules (I think that's it) to go to specific points.

Wall-to-Wall Write on Mystfit's Wall