Because the only way to make sense of anything that is happening to do with the 4th hokage is to assume people retain some level of consciousness when they are trapped inside the death god.
He has to have convinced the kyubii to be friends with him and he has learnt how to use the kyubiis cloaks in that time. Otherwise he learnt everything which took naruto the entirety of the manga and his entire life in literally minutes, despite even the best jinchurrikki like naruto and bee having to devote years of training to achieve the same thing.
He has to have convinced the kyubii to be friends with him and he has learnt how to use the kyubiis cloaks in that time. Otherwise he learnt everything which took naruto the entirety of the manga and his entire life in literally minutes, despite even the best jinchurrikki like naruto and bee having to devote years of training to achieve the same thing.