Maybe it means that the story of Harry Potter has elements that are essential to fanfiction. Such as the vivid and imaginative settings. Hogwarts, for instance, is a very distinct and captivating setting which is a big draw in fanfiction. Also, the character development in Harry Potter is quite detailed, which is another element often seen in fanfiction.
The statement could imply that 'Harry Potter' is a sort of 'elemental' or fundamental form of fanfiction. Fanfiction often takes a well - known universe and adds new twists. 'Harry Potter' already has a lot of that within its own official story. It has a diverse range of characters, each with their own backstories and arcs. This is similar to how fanfiction develops characters. And the overarching plot of good versus evil is an element that is both central to 'Harry Potter' and often explored in fanfiction.
It might be saying that 'Harry Potter' has elements that are like the building blocks of fanfiction. The magic system in the series is one such element. It's complex and unique, which is something that fanfiction writers often love to play with. Also, the themes of loyalty, sacrifice, and friendship are elements that are not only important in 'Harry Potter' but also frequently explored in fanfiction. The series has so many aspects that are like the key ingredients of fanfiction, which could be what this statement is getting at.