Looks to me that at about 4:28 in the video the situation is much too close for comfort: a glider is taking over from behind. He looks much closer than the other mentioned glider. The other pilot can not see our pilot since the fuselage in on the way. Our pilot can't see him since he is coming from behind. One small pull up or push over and.....
The other pilot must have tightened his turn to get into the center better, but shouldn't have done that close to our pilot.
Dan G