All of the description of the lighting is intended to make it plausible that the customer who comes to the astrologer late at night would not recognize him as the man who stabbed him and left him for dead. The lighting is not only dim, but is highly irregular.
It was a bewildering criss-cross of light rays and moving shadows.
Guru Nayak, the astrologer's nemesis, does not recognize him, but the astrologer recognizes Guru Nayak.
The astrologer sent a prayer to heaven as the other lit a cheroot. The astrologer caught a glimpse of his face by the matchlight.
The author, R. K. Narayan, does not tell the reader that the astrologer recognizes the customer. That is why it seems so astonishing to the reader, as well as to the customer, that the astrologer can tell this difficult and skeptical man so much about him, including his name of Guru Nayak. For a few moments the reader thinks that under the pressure of the situation the astrologer may have been transformed into a real psychic, and that such things are possible. But then it becomes clear that by the purest chance the man who wants to murder the astrologer has come to that very man for help in finding him.
This story vaguely resembles "After Twenty Years" by O. Henry, in which Jimmy Wells only recognizes his old pal Bob because Bob lights a cigar while standing in the dark doorway. In that story too, the author does not tell the reader what Jimmy sees or what he thinks, but saves it until near the end. It is ironic that a man like Narayan's astrologer, who lives by forecasting people's fates, should have his life threatened and saved by a simple turn of fate. It was sheer coincidence that Guru Nayak should come to this astrologer for advice and sheer coincidence that he should light up his cheroot and reveal his identity. Or was it a coincidence? Was it all predestined by fate and written in the stars for anyone who could read it?