I would be very very surprised if the device at 4:12 is an RPG. It looks and behaves like a long lens camera. At 4:15 you can see a space between the device and the body of the person. An RPG is also quite heavy and has a distinct shape and you wouldn't generally turn it around a corner.
As there also according to wikileaks were photographers on the scene. It's just far more likely that it's one of the front two guys who carries something that picks up his camera and take some pictures. If that is the case, then I would have to question the chopper crews ability to recognize weapons on the ground.