You can see the timings of the votes. The votes of @soupernerd exactly preceded @emilyelizabeth all voting on the same things. Largely voting on the bot @weenis but also voting down any posters who downvote that bot. Also check out all the "test" posts they both have. They are similar accounts with simultaneous voting activity.

I noticed it while my own posts started to get downvotes and I looked into it.