Leprechauns are real, man. They be stealin' mah cereal.
For all our great intelligence, we're still discovering new species of not just insects, but mammals, fish, and birds. Sometimes even in areas that you wouldn't consider deep in unexplored areas of the world.
If you threw in a fantasy level of ethereal planes (Emerald Dream), the ability for humans to turn invisible, and creatures with control over aspects of nature itself, then a lot of our stories and such could suddenly be real and our level of understanding of the world hasn't discovered them yet.
And that'd be a wild world if it were true. I imagine we'd be sending some letters questioning the cost value the tooth fairies place on our teeth. A quarter one year, 50 cents another, a dollar another and yet no consistency among us? What's up, tooth fairies, you just make it up on the spot? Let's talk standards here!
The cold truth is what's in game is considered official for canon. If the motives of a quest's implementation starts to be required prior to inclusion of it for lore consideration, we might as well argue that nothing in game supports lore until Blizzard goes through and labels everything in game as canon and non-canon facts.