Well, that user also posted over 60 links in the last year, while never receiving a single upvote or comment. I'm not sure why a flesh-and-blood user would still be posting after that.
Lo and behold, I caught it about 3 days in. Of course, I didn't even use HN for the first of those 2 days.
This day, I spend more of my time on subreddits that share HN's enthusiasm and knowledge without the subterfuge of hellbans.
I won't try to defend all of their posts; most of them are things that I don't even find interesting. But it seems that someone basically used banning as a method of cutting down on uninteresting material.
That may even be a good way of maintaining the signal-to-noise ratio on HN: if we ban the users that post many uninteresting links then the community won't have to see them. But it wasn't a tactic that I was aware of before today.