Of course, this does not mean that the upvotes also came in the same time, but still it raises suspicion of possibility of serial voting.

I have checked those answers today again. Among users with more than 3 nice answer badges, 12 out of 17 answers from this list are back to 9 upvotes. So there might have been reversal of upvotes.

I have also noticed that there is a user which yesterday has 33 votes for this week/month/day on their profile page. Today week/month shows only 19 upvotes.

I have also asked on meta.SO whether serial voting is detected and reversed on per-site-metas, too, but I take this to be a sufficient evidence that it really worked in this particular instance.