So according to her, Harry is just a figment of Ron's imagination. Being last to all his brothers in everything, unpopular and kind of a loser (sorry) he thought he'd fancy himself the Chosen One for a bestfriend.

“I mean think about it,” said Rowling. “His brothers are doing their own things, he feels pressure to be great, so he gets on the train and pretends he’s introducing himself to a celebrity and savior of wizardkind that wants to be his friend.”
Although the books are written from the third person omniscient point of view and center on Harry, Rowling says that this is a device specifically meant to imply that the books were written by Ron to detail Harry’s adventures throughout his years at school.
“One of the most classic symptoms of a delusional mind is the need to see the world in a way that revolves around yourself,” said Rowling. “In this way, Ron creating Harry, the figurative and literal Chosen One, and making this figure actively fight for Ron’s friendship at points, is the most textbook example I can imagine of a person willing to distort reality to make the universe bend around them.”
“Also, he was sad and lonely and didn’t have any friends,” said Rowling.