I originally took a Guy/Natalia fic and got the Tolstoy result.
I went in and did a find/replace all, changed "Guy" to "Harry", "Natalia" to "Hermione", and "Luke" to "Ron". Changing nothing else about the story, it says I write like Rowling.
So there you go. At least in my very unofficial experiment, it seems it's recognizing names. I'm guessing it's the "Natalia" that got Tolstoy.
Oh, then I changed them to "Robert" and "Sophie" to see if I'd get the Brown result, but it gave me Lovecraft. Again, changing nothing but the names. I'm back to my original theory--it's random for random's sake.
Also, I have 2100 words for the next part. It's almost done.