How did Sai Baba prove his omniscience to Cholkar regarding the sugar vow?

Chapter 15 beautifully illustrates Sai Baba's omniscience through his interaction with Cholkar. After Cholkar had finally made his pilgrimage to Shirdi and fulfilled his vow by distributing sugar, he was a guest of a devotee named Jog. As they were together, Baba specifically instructed Jog to 'Give him cups of tea, well-filled with sugar.' This command was profoundly meaningful because Baba did not drink tea, and more importantly, Cholkar had been secretly abstaining from sugar as a penance. This act served as undeniable proof to Cholkar that Baba knew everything about his private vow, the long delay, and the personal sacrifice he had made.