PG's comment explaining it: https://news.ycombinator.com/item?id=6596311
In fact this article does consider the flamewar detector. How accurate it is in it's claims, I do not know.
Wouldn't it make sense to remove the upvote option on the article page, surely I'm not the only one who got this wrong (I hope).
I.e. if you get to the article page from the main page, then that's fine. But if you arrive there with no referrer or from somewhere else, then it isn't counted, since quite possibly someone sent you the specific article just to upvote it.
At least that's how I understand it...