Or am I misreading and a comment has to be uncivil AND unsubstantive for it to be ban worthy?
In the above case, there were many comments that were both uncivil and unsubstantive, as well as many warnings and requests to stop, so we were squarely in the ban zone.
Incivility is worse than unsubstantiveness, so the threshold for getting banned for the former is lower. We've banned accounts that only posted fluff comments, though, since that's not the intended use of this site.
One thing HN users should know is that the substantiveness rule has an exception for empty, friendly comments such as "thank you" and "congratulations", because while those aren't substantive in content, they are salutary for the community.