What was the specific reason Dev failed to recognize Baba as the Sanyasi, leading to his delusion?

Dev's failure to recognize Baba was due to a specific sequence of events that created a mental delusion. Chapter 40 explains that the man in the guise of a Sanyasi had first visited Dev before the Udyapan invitation was even sent to Sai Baba in Shirdi. That initial visit was for a different purpose: collecting funds for cow protection. Because Dev had already interacted with this Sanyasi in a different context, he did not connect this person with Sai Baba when he returned for the meal. Dev himself later lamented this, realizing that this prior meeting was the source of his confusion and caused him to overlook Baba's specific promise that he would come with two others.