For the purposes of the filming sequence avoidance of collision would have been Viper2's responsibility, since he was the one doing the maneuvering to get the film "shot".
Flying formation one intransgressable rule was "Never take your eyes off lead", similarly in this case it would have been Viper2's responsibility never to take his eyes off Viper1.
Even with eyes on one can make errors of judgement - closure rates.