Let's be honest as an attack it has all the damage potential of your mother's moistened hanky. It is really time Rowling wrote a new press statement for the chat circuiits, she was saying the same thing when Potter first hit the news and I would happily accept that she did not think she was writing a fantasy.
Early stories bears more relationship to Enid Blyton's Famous Five, or perhaps a Dorothy Sayers whodunnit, than fantasy. Now, I would tend to consider them closer to the bitterness of Tom Brown's School Days.
The fact that she has set them in a 'magical' surround merely adds a classification for indexing. It does not necessarily make the story a fantasy as far as the writing is concerned.
Sadly, looking at the shelf of her books, she does appear to be picking up one of the more distressing trends of current fantasy and fiction writers; that of having little to say and a lot of space to say it in.