Why did the policeman on his nightly beat slow down halfway on a certain block?

In "After Twenty Years," the cop is patrolling a certain area where most of the shops are typically closed at that particular time of night. He slows down when he sees a man standing near one of the shops. It appears as if the cop is simply being cautious upon encountering a man in front of a closed shop. Before the cop speaks, the man offers an explanation as to why he is there at that particular time. He explains that twenty years ago, he and his friend were having dinner when they determined they would meet at the same location in twenty years.
While it appears that the cop is doing his job by slowing down when he encounters the man, the cop is actually the man's friend from twenty years ago. When he sees the man at that location, he knows it must be his old friend. Not wishing to arrest his old friend, he continues along his beat and has another officer arrest the man that is wanted by the Chicago police.