Normally, yes, Harry Potter would and is considered a megafandom. However, it got voted in. During the off months, NPT held an event called Lucky Number Seven where, to reward past participants who went went above and beyond by writing full length treats, pinch hits, and Hiatus fics. They got to vote in 7 fandoms from the megafandom list. Those megafandoms are: Avengers, Harry Potter, Hunger Games, Sailor Moon, Star Wars, Vampire Diaries, and X-Files.