According to Osho, he did not choose a male form at all; true spirituality is feminine receptivity, and choice itself is a function of the male ego. The outer gender is irrelevant; the inner being is a womb-like surrender to existence. From choicelessness, life unfolds as the whole; thus his form was simply what existence gave.
He didn’t pick being a man—he let life decide, because real wisdom is soft, open, and beyond outer labels like gender.