I may be wrong, but I suspect the Navy has standard procedures in place to avoid ANY unexpected obstacles (such as another sub, some debris, whatever).
And I suspect the standard procedures were not followed.
That would be my guess. Probably went too fast and without following other procedures as well. Maybe didn’t even know where they were, which would be hard to do with the inertial guidance systems we have now. Would also explain why the others were sacked as well— probably no record of their bringing up SOP or even they suggested the faulty procedures and the captain just went along.