Can you explain the story of Cholkar's vow and how Sai Baba acknowledged it?

The story of Cholkar, as detailed in Chapter 15, revolves around a vow he made to Sai Baba. Cholkar was a poor man whose livelihood depended on passing an examination. He vowed that if he passed by Baba's grace, he would visit Shirdi and distribute sugar candy. He did pass, but due to financial difficulties, he was unable to fulfill his vow immediately. As a personal penance for this delay, he gave up eating sugar entirely. When he was finally able to visit Shirdi and fulfill his promise, Sai Baba, in a remarkable display of omniscience, instructed a host named Jog to give Cholkar cups of tea that were 'well-filled with sugar.' This specific instruction, coming from Baba who did not drink tea, stunned Cholkar and confirmed that Baba knew about his secret vow and the long penance he had undertaken.