Mysterious bloody boy appears to Locke/Smokey + Richard refuses to join Locke

After Locke/Smokey frees Richard Alpert, Locke tries Richard convince him to join him. He says that he took the form of John Locke because he needed access to Jacob and Locke was a candidate. Richard reveals that he seems to know nothing about the candidates and Locke tells him that unlike Jacob, he would not have kept Richard in the dark.

Richard is clearly scared, but when Locke asks him to join him, he stand firm and says no. At that moment, Locke sees a young boy standing in a pool of sunlight with blood all over both arms. He is wearing a vest, similar to the ones the others wear. The boy clearly spooks Locke, but when Richard turns around and looks, the boy is gone. Locke then leaves Richard and says that he'll see him soon.

We'll see more screens of the boy when he makes another appearance later in the episode, but why is Locke/Smokey so scared of him?