I'll just steal one of the comments from the article. "It isn't new, and it's just as overstated as previous studies. The 80% accurate identification rate applies only within the 5,000 subjects. The identification rate will plummet when the pool of writers expands to everyone who can write in English" Like I said, if you can narrow the pool to a small amount of people, than you probably could accomplish this (but even then, there's always the chance two people have similar writing styles.)

And if you had read further, you would have seen him corrected : it's 5k words, not 5k subjects. (And, also, I do raise this potential caveat in my mention of "needles"...)