Answer:
It adds to the surprise created later when it's revealed that Jimmy did meet Silky Bob; indeed, Bob is saying these words to Jimmy himself.
Step-by-step explanation:
In the short story "After Twenty Years," by O.Henry, Bob actually says these lines to Jimmy, who does not reveal himself and is in his policeman uniform. To everyone's surprise, after Bob is arrested, he learns that the policeman he talked to on the street was indeed his old friend Jimmy, who did not want to arrest his friend.