I can't listen to that thing cos my OH is yacking on the phone. However, when my number 3 first started laying she laid 6 enormous double yolkers on the trot. I did a bit of research at the time and discovered that it happens in a young bird who is first coming into lay and whose system hasn't really sorted itself out yet. I would imagine most egg producers take in a large batch of birds of about the same age and they will all come into lay at around the same time. Thus I would imagine the chances of getting double yolkers together are quite high.
I've had no double yolkers since the beginning. Although I did have one fart egg (a very tiny egg with no yolk) during the snow, which my girls HATED.