I heard the author of the Sai Satcharitra was an arrogant and argumentative person. Is this true, and why would Baba choose someone like that to write his biography?

Yes, the author is remarkably candid about his own initial flaws. Chapter 2 describes him as having been 'mischievous, talkative, cynical, and critical,' with a 'logic-driven mind' and 'always proud of his own wisdom.' The text implies that the choice was part of a profound spiritual transformation. Sai Baba's condition for providing his full help was that the author must 'dissolve his ego and surrender it at my feet.' By choosing someone with these tendencies and guiding them through a process of surrender, the story demonstrates the transformative power of a Satguru, showing that anyone, regardless of their past intellect or pride, can become a divine instrument.