Just an illustration how much sideways skid this means. Apparently doable, but what seems unusual to me is the drift to the right, while turning right at the same time.
Usually vehicles tend to turn one way and drift the other way in the process. In case of a ground loop to the left, nose turns left, tail swings right, and the aircraft will tend to drift right.
Here the drift is to the same side as the turn. Someone must have tried to steer the aircraft to the left with the rudder, but instead of turning left, the aicraft continued to turn right due to the asymmetric thrust. What a huge struggle this has been....
With regards to why the high power setting, I read the testimony of the mechanic. His last memory is that he sits onto the turret, but he is not strapped in. Survivors reported that the landing on the MLG was hard and everything "flew forward". The mechanic came to his senses in between the pilot and co-pilot. In this case, his body may have accidentally hit the power levers, too.
B-17 approximate drift