I'm into quad-copters too. I've seen these people who race their copters through courses they can only see thru their video headset tied into the copter's camera. Wow! I've never even tried with mine. I'm too afraid of crashing it then not knowing where the wreckage is. LoL!
I watched a bts video from the producer's youtube page. In it, I saw a few shots of people deliberately walking slowly. They were either rehearsing their actions or they moved slowly as the quadcopter moved thru the shot, also slowly. In post, the video speed could be re-mapped or 'time warped' to appear normal. That way, you get hair raising close encounters with people without much risk of hitting them or crashing the copter. Same thing with the copter whizzing by while just missing support beams as it quickly zig zags between them.. I don't know if that's what they did, but it would make sense.