I think you misunderstand what [flagged][dead] means on HN. It typically means that other users have flagged the submission, and once a certain small number have done so (2? 3? something like that) it is marked as [dead]. At this point is visible only to the moderators, and to users like me who have [showdead] on in their settings. Users with a certain number of points (500?) can then vouch for a story to bring it back from the dead---at least until more users flag it and kill it again.

So in this sense, yes, HN actively censors all sorts of things. But usually it's done by users, rather than by the moderators. If you turn on [showdead] yourself you can see which things these are. I'd roughly guess that about 90% is straight up spam that should definitely be flagged, 8% are debatable depending on what you think should be here on the site, and 2% are wrongly flagged. Obviously, different users will sometimes disagree on which category a post falls in.

I'd put your original post in the "debatable" category. I wouldn't have flagged it myself, but I don't feel confident in vouching to try to revive it. This isn't because of the subject matter, but because I personally don't feel comfortable with hoax calls like that. I suspect Google doesn't either, and this is probably why they removed it. Or possibly I misunderstand their premise---I haven't watched the video.

The last two, including this one, were more likely flagged because you are creating posts to complain about site moderation, and that's essentially against the rules. I vouched for this one to revive it so that I could respond to you. If you have comments about site moderation, they are better done via email with Dan: hn@ycombinator.com. He's very busy, but generally very good at responding eventually to polite inquiries.

As old as your account is, you should know how Hacker News works by now.

If you have questions about moderation, the email link is in the footer.