Poor consumptive boy
That poor boy is suffering from consumption. According to Ruby Glenn's story, he is “always hanging around the station”1 where Joe Glenn works as an telegraph operator. On one side he seems to have a lot of time on his hands, because he is spending a great deal of his time around the railway station. On the other side it could also be the result of some sort of fascination over trains.
It does not become clear why he was willing to help Joe Glenn out that day. It could either be a respect for authority characters (even though Joe has a week character, from the boy's perspective he is a man who has control over trains), or a willingness to help which makes him feel needed, or the opportunity itself to finally be in charge of a matter. Having control over something is important if the reader keeps in mind that the boy cannot control his illness. He is completely and utterly at the consumption's mercy.
After preventing a catastrophe from happening, he goes back to “his father's farm out in the country, and before Christmas he [is] dead.”2 He dies without ever being thanked for what he has done. His deeds are never acknowledged. Only after the boy's death does Joe Glenn tell the directors the truth.