Likely when the TES construction set came out people explored the information data base and found it. Also there is the console of which you can do a limited amount of poking around. There are many ways to accidentally find something as well, I've discovered things by kicking them and noticed they had a strange name instead of "yet another clutter amulet". Easter Eggs are oft hidden that way. For example the corpse in the water above Fort Nikel has nary a mention in the game (and has a rather lore breaking name). However there it is, floating. Unless you walk across it you would be wholly unaware it was there.