Earlier quoted context omitted.
> For example, maybe you could explain the full backstory of why this post was killed: https://news.ycombinator.com/item?id=12313089 . I can explain it. It says right there that it was [flagged]. Enough people hit the "flag" link to automatically kill it.
That's the usual answer, but I think there may be more happening here than that. One slight oddity is that there was no "vouch" button visible to me on the dead comment. This made me wonder if there was a separate mechanism in play here. Out of self-interest, it also made me wonder if maybe my "vouching" privileges have been removed. Separately, although multiple flags can kill a comment, it's still subject to modera…
The vouch button appears for me.
> and on what basis they were flagging it.
I didn't flag it, but it contains some deliberately provocative phrasing from someone who's previously had user flags (and a ban) for their posting style.
In particular:
>> the original post which dang replied to and subsequently killed.
These comments tend to attract downvotes and flags because they're untrue. For one thing that post doesn't appear to have been killed, and if it had been killed it probably would have been user flags, not mods, that did the killing.