Can you explain the whole story of Dev's Udyapan ceremony and why he initially felt deceived by Sai Baba?

Dev invited Sai Baba to his Udyapan ceremony, and Baba promised to attend with two other people. However, on the day of the event, Dev was disappointed because he did not see Baba arrive. As detailed in chapter 40, a Sanyasi with two companions did show up uninvited, was served a meal, and then left. Feeling let down, Dev wrote a letter to a man named Jog, complaining that Baba had broken his promise. Jog relayed this message to Baba, who then revealed that he had, in fact, attended the ceremony in the guise of that very Sanyasi. When Jog informed Dev of this, Dev was overcome with emotion, feeling ashamed for doubting Sai and failing to recognize him.