Thrusty One
No, I don't think there is any chance that the engine was allowed into reverse. The effect you saw is down to the extreme flow disturbances that would have occurred as the gas generator casing was basically blown open as the engine was still alight, there would have been flame coming out of the ruptured IP turbine case and no doubt the engine would have surged thus causing the internal airflow to reverse at least once. The sooting shows that the hot fuel-rich gas escaped through the small gap where the damaged nacelle moved relative to the fan case after the aft portion was blown apart by the departing turbine disc piece.