It's not just the stolen account element: he's randomly voting up posts at 100% strength. Other large stakeholders don't normally do this, unless it's a really good/important post, because they influence rewards too much by doing so. Instead they vote a smaller percentage.

Random 100% votes from a large stakeholder end up distributing the rewards unfairly. Maybe you're not aware of this, but every downvote distributes the downvoted rewards to other posters. Downvoting his super large random votes counters this unfair distribution. And I don't even fully counter them, I just reduce their strength some: you can see this by noting that his vote is higher on the list when you look at voters.

Now it's true that the posters are sometimes confused/upset by this, because they don't understand the system. But once I've explained it to them, most seem to get it. I do wish the vote bot I use for this allowed me to leave an explanatory message, and hopefully @howo will have some time in the future to support that feature in the tool.