Why does the book discourage argumentation but then immediately bring up the author's argumentative past when introducing the name "Hemadpant"? Isn't that a contradiction?

This is not a contradiction but a deliberate narrative technique. As detailed in Chapter 2, after Sai Baba's words "Do not engage in dualistic explanations," the author is reminded of his promise to explain his name. By immediately recounting his own past as someone "prone to argumentation" and with a "logic-driven mind," he provides a powerful, personal example of the very state that Sai's teachings help one transcend. This sub-story, described in Chapter 2, serves to illustrate the author's own journey from ignorance to devotion, thereby reinforcing the main message against pointless debate by showing its negative origin and the path away from it.