In what sense was Nietzsche a psychologist?

Answer 1

Primarily, in the way that he predicted the results of man's plunge into the abyss of nihilism.

The essence of his theory has to do with human behavior in attempting to deal with the consequential aftermath.

Answer 2

Nietzsche stated “A man without a plan, is not a man.” And a lot about the effects of Christianity on a person, which could be construed as psychology.