The switch had to be operated deliberately, but still a UX fail on a modern aircraft if cutting off fuel to the engines does not result in an audible alert/alarm which both pilots can hear - especially at that altitude.
It would not make any difference. They were too low and did not have enough time to recover. They immediately switched back to on. Two captains is discussing it here (https://www.youtube.com/watch?v=SE0BetkXsLg).