Writing is usually a rather solitary activity. But writing for publication can be understood as extraverted in spirit, and actually publishing one's writing is extraverted in spirit.
For the sake of discussion, let's use the terminology that Jung uses and say that Nietzsche was experiencing the Dionysian spirit in his unconscious and that this helped him to write the works he completed in the 1880s.
But just how healthy is it to live in such close proximity to one's unconscious for several years? Granted, Nietzsche had a laundry list of physical ailments that compounded his life.
In connection with the character Zarathustra, Jung claims repeatedly that he represents the archetype of the wise old man. In constructing his commentary on Nietzsche's book, I would suggest that Jung is drawing on the archetype of the wise old man in his psyche.
Even though Jung is wordy and digressive and sermonic, he is a good guide to Nietzsche's puzzling book. But take him with a grain of salt.