I love the whole ‘Earth is space Australia’ thing, so here’s my contribution.
What if aliens don’t have fiction? What if everything they document is pure fact. And they assume that humans do the same.
These aliens already fear and respect humans. After all, humans will do anything to survive, protect their friends, they can bond with literally anything, live in anything from sub-zero to halfway to boiling temperatures, take risks 'for fun’ or 'to see what would happen’, they can and will keep going under pressure and if injured. They are extremely creative and can find a solution to get out of any situation. Nothing can stop them once they have their mind made up.
Humans. Are. Terrifying.
And then aliens come across human fiction. Except they don’t realize that it’s not real.
Imagine their surprise when they learn about mythological creatures and supernatural beings. Imagine their astonishment when they discover that humans have survived many, many apocalypses. Imagine their fear when they realize that a rather large portion of the species has powers whether through a mutation or straight out magic.
Imagine their horror when they realize that humans could easily take over the universe if they ever felt like it.
Aliens passing the word around, telling of the great feats of 'Superman’, 'Matilda’, 'Neo’, 'Korra’, 'Potter’.
And then comes the question: why haven’t the humans taken over? What could possibly be stopping them?
Maybe, the aliens surmise, the humans don’t realize how simple it would be to take the universe for themselves. Many aliens beleive that this theory is correct and swear that they’ll never bring it up to a human.
Others think that humans just want to be friends with other species and, seeing as aliens are already terrified of them, decided to keep their abilities a secret.
Of course a few aliens outright ask the humans why aren’t they using their 'secret abilities’. And they receive two very different answers. Some humans laugh and say that they don’t have any powers. That their 'documents’ are fake. And then there are the humans who that like to mess with the aliens and say that they are 'sworn to secrecy’ or that they are 'biding their time’.