That account isn't banned, and what you said about new accounts definitely isn't true.
HN has a lot of anti-abuse software. It's possible that you saw some of its effects and drew an over-general conclusion.
You and anyone else are welcome to email hn@ycombinator.com if you have questions about what's going on with your account. We're happy to answer questions, and to roll back bans or penalties when people give us reason to believe they will use the site as intended.
But s/he's made two comments, and neither has been killed. Both are heavily down-voted, but that's not the same.
Even so, if anyone keeps getting shadow-banned then I'd expect that they'd learn how to make comments that don't get them shadow-banned. If they just keep banging against the moderation without changing their behaviour and without adapting to the community, maybe they really don't belong here.
<fx: shrug />
Finding it hard to care, given the comments I've seen.
Speaking from experience and experiments here.