According to the article, they are betting on Betfair. When the race starts, you have a delay in placing new bets (5-10 seconds) but no delay in cancelling bets. Given they are ahead of the official live feed by just few seconds, it should leave enough time for a misplaced bet to be cancelled before they can take it. I am quite surprised they have an edge here, I might miss something.
The delay is 1s for placing bets inplay on racing, you are correct in regards to zero delay on cancellations. The advantage is simply down to latency and being ahead of everyone (except GPS users) in an event where probabilities move very fast. A lot (maybe the majority) is liquidity provided by automated systems or ’keep’ bets placed before the race where the user has no intention to cancel.
