Even if he was able to get to a hose and remove the somewhat settled concrete there would have still be damage. Granted it wouldn't have been as bad, but it would have still been noticeable. Rocks and sand don't magically float on a small sheet of water and thus would have been pushed across the surface anyway leaving behind marks as they went. We arent even going to discuss what the finish would have looked like had it been able to set further or had he drove away leaving it on there to be pushed by the wind under acceleration.
