The popularity of Harry Potter and the fact that it has inspired so much derivative work could lead some to think it's a fanfiction. It has such a large and passionate fan base that has created countless stories, art, and interpretations based on it. This makes it seem as if it might be part of the fanfiction realm, when in fact it is the original work that inspired all these fan - made things.
Some people might think so because of the use of common fantasy tropes. For instance, the idea of a young hero in a magical world facing great challenges. These tropes are also present in some Warren fanfictions, so they may draw the comparison.
One reason could be the way Harry Potter observes and gathers information. Rangers are good at observing their surroundings, and Harry is often in situations where he needs to do the same. In his search for Horcruxes, for example, he has to be very observant of the places he visits and the people he meets. This aspect of his character might remind some people of the skills that a Ranger would possess, thus leading them to think that Harry Potter has elements of a Ranger fanfiction.
Some people might think Harry Potter is apathetic in fanfiction because the writer wants to explore a different side of his personality. Maybe they want to show how he could be if he had different life experiences. As for being a 'pet', it could be a really odd or creative interpretation where the writer focuses on his relationship with his owl Hedwig in a very extreme way. But these are not typical views and are more of the result of some very out - of - the - box fanfiction ideas.
Some people might think this because of the common theme of a young hero on a journey. In both, there is a central character who has to face great challenges and grow throughout the story. Also, the use of magic or some form of special powers is present in both. In Pendragon, there are powers related to the different worlds and in Harry Potter, there are spells and magical abilities. This similarity in the basic structure of the story could lead to such a thought.
The magic system in Harry Potter might be a reason. It has some similarities with the mysterious and unruly nature of fae magic in some fanfic ideas. For example, magic in the wizarding world can sometimes be unpredictable, like fae magic.
Some might think so because of the theme of a 'chosen one'. In the Noah story, Noah was chosen by God to save the animals and his family from the flood. Similarly, in Harry Potter, Harry was the chosen one to defeat Voldemort. But this is a very basic similarity and doesn't really make it a fanfiction.
People may think this due to the fact that both deal with a form of power that is not fully understood by the outside world. In Harry Potter, magic is a powerful force that only wizards and witches can truly master. In Atlantean lore, there was often some sort of super - advanced knowledge or power that was associated with the lost city. But really, these are just broad similarities and not enough to label Harry Potter as Atlantean fanfiction.
Some might think so because of the out - of - this - world and often zany elements in Harry Potter. Just like in a flounder fanfiction where the author might come up with really strange and unique ideas, in Harry Potter we have things like talking portraits, flying broomsticks, and magical spells. These elements are so different from the normal world that it could give the impression of being part of a more off - the - wall fanfiction.
Draco Malfoy is quite popular in fanfiction. Sometimes he is redeemed and becomes friends with Harry and the gang. His complex family background and his own internal struggles make for interesting storylines. Another popular character is Luna Lovegood. Her unique view of the world and her kindness can be explored further in fanfiction, like she might lead a group in exploring some ancient and forgotten magic.
One interesting story could be about Harry having a secret adventure during his summer break that wasn't in the original books. Maybe he discovers a hidden magical creature in the Forbidden Forest and has to protect it from dark wizards.