Why do you think the author called the story "An Astrologer's Day"?
There seem to be two stories taking place simultaneously in "An Astrologer's Day." One story is about the strange coincidence of the astrologer encountering the man he thought he had killed some years before. But the more important story is the implicit one about the incredibly hard lives of the poor in grossly overpopulated India. It concerns the modern phenomenon of country people moving into the big cities all over the world, and then having to survive from day to day with a few coins collected any way they can. The astrologer has a good day financially, but he really only brings home enough money for food and a little extra treat for his daughter. He is dealing in coins comparable to our pennies. The passers-by don't have any money. If they weren't so poor they wouldn't be passing their leisure time just walking in a public park and stopping to gape at any sideshow along the way. The astrologer's so-called "professional equipment" is paltry and tawdry. He may have acquired it from another astrologer who gave up the struggle--or died of starvation. The astrologer has plenty of onlookers, but these poor, simple people would stop and look at almost anything out of curiosity.
...and his eyes sparkled with a sharp abnormal gleam which was really an outcome of a continual searching look for customers.
He is surrounded by men, women and children, and there is an endless stream of others passing by--yet he is continually searching for a single customer in the throng.
Narayan titled his story "An Astrologer's Day" in order to suggest that life was a continual struggle for this one man, just as it is for countless millions crowding into the big cities. Tonight and tomorrow the astrologer and his family will eat because he has managed to collect a few coins. But there will be other days in which the little family may go hungry. And what if it rains? He will worry about that tomorrow. The story ends on a note which shows that the protagonist is philosophical about existence. At least he has managed to find his own little exclusive niche in this cruel world.
"Time to sleep," he said, yawning, and stretched himself on the pyol.
I think the author named the story this way because it fits the nature of the themes that were to be addressed. To be more specific, Indian society (as Narayan portrays it) is concerned with fate, and requires people to read signs well to determine their actions. As a writer, on a practical level, this also gives reason to investigate any action, and to "read" (interpret) any event for meaning.
The title is factual, since the story concerns one day in the life of the astrologer's life. However, it also achieves understatement and a bit of irony. It might have been one day in the man's life, but it certainly wasn't a normal one. Through a strong twist of fate, his life changed profoundly on this one day.