This quest never shows up in the journal, it all happens on it's own. You don't have to read the journal, and you don't have to go after the monster. However, if you do read the journal, it still doesn't go in your journal, and you get no help finding the monster. This sort of free-form quest is exactly what needs to happen a LOT more in future TES games. While there wasn't much to this quest, it is still one of my favorites, if not simply for the fact that you do it all on your own.
Please, let Skyrim be full of quests like these!