As a non-horse person, who has watched the video.
The behaviour shown is not a rare error of judgement, or someone momentarily losing control. That is absolutely relaxed, casual, routine, something CDJ has done a thousand times before.
Those speculating about motives and sabotage. My first thoughts are a then-underage rider, mid-teens, distressed at what is happening, but unsure what to do. Possibly conditioned to think it is normal and fine. Or whose parents, who pay for everything, are up to their neck in it, and possibly even the vile cackler. Or whose family are non-riders, unable to advise or support.
A teenager, unsure, distressed, idealistic, unsupported, but now of legal age, awash in riding buzz about CDJ and Olympics and medals and damehoods, in turmoil and disgusted and now determined to do something. Brave.
That's my interpretation, but again, not a rider.
Whatever their motives, I'm thankful.