Yeah, and it can take a surprisingly small amount of flags to take down a post. So it could literally just be a dozen people flagging them, not even in a coordinated matter.

Something similar happened on Jan 6 this year with a lot of individual users being like 'No, this isn't related to tech, so we'll flag it." until a couple posts got enough traction to actually stay at the top.

BTW, you can 'anti-flag' by vouching a submission. I've done this a few times when HN insta-flags posts about inclusion in tech.