The users of those posts aren't necessarily hellbanned - the posts are though. If enough people flag a new story I think it'll automatically be marked dead.
Usually it's just for spammy crap, or stories that aren't very interesting.
https://news.ycombinator.com/item?id=6155513
I don't think many stories get flagged just on the new page. It's usually domains that are flagged, like buzzfeed.com, huffingtonpost.com, or gawker.com. It sounds like maybe there was a bug in the server today.
In this case, it's part of a policy not to discuss meta-hn issues on hn. If you start a post asking why you were hell banned, or flagging/downvoting, it'll usually get flagged and/or removed.