opening of Chimps & Blimps (novel using setting & characters of Transmontane Run) - Margaret Atwood
opening of "On the Transmontane Run with the Aerial Mail Express" - Mark Twain
opening of unfinished Boxer Rebellion story - Mark Twain (damn! I was aiming for Kipling)
cut scene from The Willow Knot - Neil Gaiman
opening of The Cost of Silver - James Joyce
2d chapter of Trading in Ghosts - James Joyce
opening of Bookwyrms - H.P. Lovecraft
opening of Children of Mercury - Dan Brown
opening of unfinished True Heir story - Rudyard Kipling
I think the program is using keywords, rather than anything really diagnostic like sentence length and complexity, paragraphing, etc.
Bookwyrms is written quite straightforwardly but includes the words 'curse' and 'shamanic'. The cut scene (a couple of entries below, actually) has 'charms', the opening of Transmontane has 'I reckon' and 'tall tales', the Trading in Ghosts chapter has some bad words, and Mercury is set in a medieval Italian painter's studio (though there are no codes and Leonardo hasn't been born yet).