(https://news.ycombinator.com/item?id=13094354 is the comment, which I find entirely reasonable but obviously people disagreed, or at least it was considered off-topic)
There is no reason, based on the HN guidelines, that the referenced post should have been downvoted, let alone flagged. Whoever did so abused their power to make such decisions.
This "drive by down-voting" happens regularly here. I've had comments downvoted within seconds of posting--clearly the voters could not have had time to read the entire text. They see a few key words that trigger them, hit the arrow, and move on to the next job. Unfortunately, there's no way in JavaScript to tell whether someone's actually read the thing they're down-voting, so we get these knee-jerk keyword-based brigades.
To test this, sometimes I'll write something where the first sentence is provocative, but the rest is (I hope) a solid, nuanced argument. Usually it's at -1 or -2 within a minute, and then over the next few hours slowly crawls back up to +2 or +3 as people actually read it.