According to the text, what was the specific reason Dev failed to recognize that the Sanyasi was actually Sai Baba?

Dev failed to recognize Sai Baba because of a prior, unrelated encounter with the same Sanyasi. Chapter 40 explains this crucial detail from Dev's own perspective after he learned the truth. Before Dev had even invited Baba to the Udyapan, the Sanyasi had visited him to collect funds for cow protection. Because this initial meeting was for fundraising, Dev's mind had already categorized the Sanyasi in that context. When the same person appeared at the feast, Dev's perception was clouded by this pre-existing "delusion." Dev lamented, "he came for cow protection to get funds; after that, the invitation for the Udyapan went to Sai. Therefore, such a delusion fell."