This doesn't mean necessarily that there is a single person doing it. There is a simpler explanation using the LW mechanics: You see a noteworthy post (for whatever reason) and you want to know more about it. Naturally you click on the author an see lots of his comments. If you are rigorous it is natural to vote them all. If you generally disagree with them it is likely to look like a block downvote - what it is but not on priciple ground but simply because the it is a on-person batch operation facilitated by the LW UI. This can also happen the other way around. block upvotes. I seem to have noticed that I get some of those every now and then (and not necessarily directly following a post). I did this kind of looking at peoples contributions too. And surely I did block upvotes. No block downvotes but I could have.