Can you explain how Sai Baba actually attended Dev's Udyapan ceremony? It seems like Dev missed him.

Yes, Dev did not recognize Baba's presence. According to the account in Chapter 40, Sai Baba fulfilled His promise to attend Dev's Udyapan ceremony by appearing in disguise, not in His usual form. Baba explained to Jog that He first made a solitary appearance as a Sanyasi, during which Dev worried that the guest would ask for money. Later, true to His word that He would come with two others for the meal, Baba returned in the same Sanyasi guise accompanied by two companions. These three uninvited guests were served the meal by Dev himself. Baba's statement, "I said I would come with two others, and I went with two others," confirms that He kept His promise precisely, but Dev's lack of perception caused him to miss this divine leela.