The starter may have called the start off, as is required when a horse is facing the wrong way, rather than C Alford "stopping the start".
If the mobile had only just started rolling I could see how the starter could recommence a start if the remaining horses maintained some sort of orderly formation. The possibility of that - the starter and chief steward, who is communicating with the starter, try to avoid the race being booted to Sky2.
Just an interpretation, only watched the race on Sky.
