How did Sai Baba actually fulfill his promise to attend Dev's Udyapan, and why didn't Dev realize it?

Sai Baba fulfilled his promise by appearing at Dev's home in the form of a Sanyasi, accompanied by two companions. Chapter 40 explains this entire sequence of events. The Sanyasi first approached Dev for a donation for cow protection, was turned away, and then returned a month later asking not for money, but for a meal. Dev hospitably fed the Sanyasi and his two friends. However, Dev failed to realize this was Baba's visit because his perception was clouded by Maya. He was expecting a more direct or recognizable appearance, and the unexpected nature of the Sanyasi's visit left him feeling that Baba had not kept his word, leading him to express his disappointment in a letter to Jog.