In fact, it was: https://twitter.com/mjg59/status/527890332206510080
Call that "penalized" if you want, but it has nothing to do with the content, so that tweet is misleading—and ironic, too, given what provoked the "penalizing".
(Also, in case anyone's wondering, moderators haven't touched the post.)
The obvious definition would be a clique of accounts that all upvote each other's stories, but that seems rather unlikely in this case; is there a secondary criteria? Are you looking to prohibit what Wikipedia calls "meatpuppetry"? Are you also looking to prevent upvotes from people who reach an HN discussion via Twitter or other sites?
But let's say what good voting means to HN. It means voting for something that you personally find intellectually interesting, regardless of who posted it and regardless of what you or your friends are hoping to promote.
Do certain types of content set off the ring-voting detection more frequently? The type of content likely influences how it's shared and how people respond to it, which would affect how it's voted (and/or flagged). Algorithms are not unbiased, particularly when no one's bothered to study their confounding factors.
Sure—people posting their startups, for example, set off the ring detector more frequently than the typical news article. Friends voting for friends' blog posts, too. But is that a bias of the algorithm? That strikes me as a stretch.
(i.e. a subgroup of people who all love, say, Lisp, and therefore always vote up Lisp stories. They're not an organised group - but they do tend to vote in concert.)
Sure, many article at the top of HN after often posted elsewhere (e.g. today) because they are incredibly newsworthy.
However, a HN post that people share on social media network for the purpose of upvotes is a different story.
There's a difference in motivation between "check this interesting article out" and "please upvote me", but the ring-voting detector can't necessarily tell the difference.
In the former case, why would they be linking to HN in the first place, instead of the article itself?
HN has a basic voting ring heuristic to ignore votes from direct links to HN submissions from a non-HN referrer for this reason.
At a minimum, I would tend to put something like this: interesting article (link to article) via HN (link to HN).
Though I'm certainly less likely to do that now that I know that HN does not like such links.
I don't think it's appropriate to post something like that about one's own story, but for a story you found interesting and want to share, I think it makes sense.