Why specifically was Dev so confused and unable to recognize Baba when he appeared as a Sanyasi?

Dev's confusion stemmed from a specific prior encounter with the man who appeared as the Sanyasi. As Dev himself reflected in Chapter 40, his delusion was caused by the fact that this same person had previously visited him to collect funds for cow protection. Because that first visit was for a worldly purpose and happened before Dev even extended the Udyapan invitation to Sai Baba, Dev's mind created a separation. He saw the Sanyasi merely as a fundraiser returning for a meal, not as the divine guest he was waiting for. Dev admitted that if the Sanyasi had only appeared for food after the invitation was sent, his "vision would not have been so confused." This preconceived notion acted as a veil, preventing him from recognizing Baba.