Why did our prophet (ﷺ) get annoyed when being asked about his fasting in muslim 1162?

"Abu Qatada reported that a person came to the Messenger of Allah (ﷺ) and said:How do you fast? The Messenger of Allah (ﷺ) felt annoyed. When 'Umar (Allah be pleased with him) noticed his annoyance, he said: We are well pleased with Allah as our Lord, with Islam as our code of life, and with Muhammad as our Prophet. We seek refuge with Allah from the anger of Allah and that of His Messenger. 'Umar kept on repeating these words till his (the Prophet's) anger calmed down. ..." Reference: Sahih Muslim 1162.01 In-book reference: Book 13, Hadith 252