I don't think you're fully appreciating the context here... The moderator of that community had been trying over and over, both privately and in public, to get this person to follow community norms for years, but they just would not do so.

To me, who has been in that community for years, it was entirely the correct action to take. Moderation is hard and no fun at all, but it needs to be done, or else a community will descend into madness.