It's the software that tries to catch promotional votes a.k.a. voting rings. It does sometimes get things wrong, which is probably what happened here.

As sctb said, though, it's user flags that affected the post's rank the most. Perhaps the editorialized title had something to do with that (https://news.ycombinator.com/item?id=18097611), and/or perhaps there is just fatigue with this class of submissions. People come to HN for unpredictable things, so whenever something starts to get predictable, they get ornery.