The text says the author is just a 'pretext' and that Sai Baba would write his own story. How can we be sure this isn't just the author's own interpretation or ego speaking, especially when he's writing a biography?

The source material addresses this concern directly. According to Chapter 2, Sai Baba Himself gave the instruction, stating, 'He is merely a pretext; I myself shall write my own story!' The condition for this divine authorship was the dissolution of the author's ego. Baba clarified, 'He should dissolve his ego and surrender it at my feet... When the ego is dissolved, no trace of it remains. Then I myself shall enter with 'I-ness' and write with my own hand.' Therefore, the text presents the work not as the author's interpretation, but as a divinely inspired act where the human writer is simply a surrendered instrument.