An analyst somewhere who isn't aware that people are literally playing with the test buckets and jumping between them to figure out what the query parameters do is going to write a confident report on why A outperformed B.
For example, the param may point to specific time on the video.
Or the param may point that the video is part of some playlist, so that when somebody clicks he is brought not just to the same video but also to same playlist.
As we don't know anything about this particular param we don't know if it is the case.