When Flocke sees the ghost boy, he seems genuinely frightened. This encounter did not seem any different than the many other visions or ghosts or horses or Hurleybirds that people on the island have seen in past episodes. All this time we have been attributing these strange encounters to the smoke monster, but how can that be the case if the smoke monster himself has his own vision/encounter?
This makes me think that there is some other force on the island (or the island itself) that makes people see strange phenomenon, usually something that's haunting them from their past. Flocke seems to recognize this boy and is being haunted. He is not the one doing the haunting...so maybe it has not been the Smoke Monster all along. Maybe he is not the one responsible for Eko seeing Yemi or Kate seeing the horse or Hurley seeing Dave.