Both the featured doc and the other one I linked elsewhere in the thread cover that sequence. The people were filmed from the News Chopper. It's kind of obvious they had been told to "mill about" for the camera. They just walk in circles, going in one end of the building and emerging from the other and circling back around. From a zoomed out shot you wouldn't have been able to tell, it just looks busy with people. But the Chopper cam zoomed in for long enough to spot it.