What is surprising to the signalman when the narrator calls to him in "The Signal-Man"? Why?

When the narrator calls to the signalman, the man has something "remarkable in his manner. . . His attitude was one of such expectation and watchfulness," as though he is wary of the narrator. It is as though he has seen the narrator before and is afraid of him.
Once the narrator descends and talks with the signalman, the man reveals to the narrator that his calling down from above has reminded the signal-man of an apparition he has seen before because the narrator called out the very words of the apparition. Hearing this in such a dismal, dark, and lonely place, the narrator wonders if the signalman himself is not some sort of apparition. Nevertheless, the narrator establishes a relationship with the strange man, who describes his job to him. Further, the man confides in him that he has seen a man covering his eyes and his right arm who waves violently and calls out, "For God's sake, clear the way!" 
Shortly after this conversation, the narrator sees what seems to be an apparition at the opening of the tunnel. The man stands with his arm over his eyes; he waves desperately at the mouth of the tunnel. After he runs to the signal box, he is informed that the signalman has been killed by a train that morning. Eerily, just as the signalman described his apparition, a man covered his eyes to prevent himself from seeing the train run over the signalman.
The narrator asks the men around the opening of the tunnel what has happened. "Signalman killed this morning, sir," one replies. "Not the man I know?" the narrator asks fearfully. When he is brought to the poor, dead man, the narrator asks how his death has occurred, and the men describe exactly what has happened to the signal-man. It is eerily familiar to the narrator.
"What did you say?" the narrator asks the engineer. He replies, "I said, 'Below there! Look out! Look out! For God's sake, clear the way!"
Shaken, the narrator realizes what occurred is exactly like what the ghostly apparition has done as described by the signalman.