They weren’t attempting anything, just repositioning for the next pass. They were flying away from the audience. They lost track of each other.

The video, apart from the apparent loss of situation awareness by the following pilot, seems to show the leader making an aggressive left turn basically into the path of the other aircraft. I'm four hundred miles or so from the location but we've had some weird weather here today, and I've heard it was even more weird in Idaho. Reports of high wind speeds and gusts. I wondered if the lead aircraft had been hit by some sort of atmospheric event that pushed it into the path of the other when it happened to be too close to correct.