Why was Dev so confused and doubtful about whether Baba had actually come to his feast?

Dev's confusion stemmed from his failure to recognize Baba in the form of a Sanyasi. As Chapter 40 explains, this particular Sanyasi had previously visited Dev to collect funds for cow protection, well before Dev had even invited Baba to the Udyapan ceremony. Because of this prior encounter, when the Sanyasi returned and asked for a meal, Dev simply saw him as a guest arriving for his own purposes and not as Sai in disguise. Dev later lamented his own delusion, admitting he forgot to pay attention to Baba's specific words: "When I come for the meal, two others will come with me." This oversight, combined with the Sanyasi's previous visit, caused Dev to doubt Baba's promise and write a letter of complaint to Jog.