How did Sai Baba confirm Kakasaheb Dixit's private vision of Vitthal?

Chapter 4 details a profound incident where Sai Baba demonstrated his omniscience by confirming Kakasaheb Dixit's private spiritual experience. After Kakasaheb had a vision of Lord Vitthal during his morning meditation, he went to see Baba. Without being told anything, Baba immediately validated the experience by asking him, "Vitthal Patil had come, right? Did you meet him?" Baba even offered advice, telling him to "Nail him down and make him steady," implying that he should hold onto that divine vision firmly. The confirmation was made absolute later that day when a traveling seller arrived with pictures of Vitthal, and one of them was an exact match for the form Kakasaheb had seen in his meditation.