Did Sai Baba actually attend Dev's Udyapan ceremony? I thought he didn't show up.

Yes, Sai Baba did attend Dev's Udyapan ceremony, although Dev did not recognize him at the time. As Chapter 40 explains, Baba had promised to come with two others. He fulfilled this promise by appearing in the guise of a Sanyasi, accompanied by two companions. They arrived at noon, were served a meal, and then left. Baba later confirmed this to Jog, stating, "I said I would come with two others, and I went with two others." Dev only realized this truth after Jog sent him a letter detailing Baba's explanation, which filled him with remorse for his doubt.