It seems like Sai Baba deliberately deceived Dev by coming in a disguise. Why would a saint play such confusing games with a devotee who invited him with love? Wasn't it cruel to let Dev feel so disappointed?

According to the account in Chapter 40, Dev did feel deceived and disappointed when he believed Baba had not kept his promise to attend the Udyapan ceremony. He wrote a letter to Jog expressing his confusion and feeling that Baba's words had "turned out otherwise." However, when Jog presented this to Sai Baba, Baba explained that he had indeed attended in the guise of a Sanyasi along with two other people, just as he had promised. Baba reframed the situation by questioning Dev's perception, asking, "tell him, 'You did not recognize Me! Why then did you call Me?'" The text suggests that a "veil of Maya" and Dev’s own preconceptions prevented him from recognizing Baba, rather than it being a cruel game. Baba stated firmly, "for the sake of My word, I would die; but the words from My mouth shall never be otherwise."