The typical scenario is loss of an engine after Vmc but before the best single-engine rate of climb is achieved. If the crew was late getting the gear up and setting a lower than normal positive attitude to allow the aircraft to accelerate to the single-engine rate of climb airspeed it may not have climbed at all. At the end they may have tried to force it up, decayed the airspeed to Vmc, and it rolled. Not saying at all that's what happened here but it has happened in the past.