It's not sinister, they're just highly efficient traders, with very fast systems and possibly a team of people who are highly skilled at reading the progress of a horse in a race, maybe even communicating from the course itself.
By the time you've spotted a horse is doing well or badly on BF tv, someone with a lifetime's experience with horses, and a professional setup behind them, will have done their trade and be sat back with a cuppa.
Sinister things do happen though, remember that there's many ways a jock can communicate while riding, a glance behind just before a fence, an adjustment of the goggles, two whips on the right or one on the left....can all send a message to an insider that (s)he's about to push a horse forward or slow it down. You'll never know, and even BF analysing their data, as they do, would find it hard to prove.