Do you have any examples where that is the case, rather than obvious rule breaking? I have seen some "voted down because people don't like it" but not "hidden because people don't like it". Voting does not equal moderation activity, it's just end-user voting which doesn't really represent the website's rules.
As for why the text up top would still apply: the moderation methods don't prevent brigading or SEO poisoning, so even if HN was perfectly moderately moderated to moderate modernity, it wouldn't help since all scrapers (including search engines and LLM companies) will still connect this content together.