EXPLAINED: He made no contact with Russell so why did Alonso cop a 20-second penalty for his part in the crash?

Fernando Alonso has been hit with a post-race drive through penalty converted to 20 seconds being adding to his race time for what the stewards have deemed potentially dangerous driving prior to George Russells crash out of the Australian Grand Prix on the final lap. There was no contact between the two, so what was the story behind the penalty? Lets delve in to break it down¦