How did Sai Baba show Cholkar that he knew about his secret penance?

As described in Chapter 15, after delaying the fulfillment of his vow, Cholkar gave up sugar as a form of penance, even drinking his tea without it. When he finally visited Shirdi and had his darshan, he was a guest of a man named Jog. As they were about to leave, Baba specifically instructed Jog, "Give him cups of tea, well-filled with sugar." This was a profound moment for Cholkar, as Baba did not normally drink tea. This specific instruction showed Cholkar that Baba was omniscient and fully aware of his secret vow and the personal sacrifice he had been making.