I was at the start hut when this was taken and saw your flash going off, i wondered "why is he using a flash in this sunshine?" and now i know Awesome shot mate!
The sun is behind Greg so without flash there is a choice between a correctly exposed sky with an underexposed silhouette of the rider, or a correctly exposed rider and a featureless white sky. With a high powered flash I can overpower the sun to get both sky and rider correctly exposed and pin sharp.