Likely was a bot from someone socking. I toyed with the idea of using ghost neg-rating to troll forums and abuse the points based nature of discussions, but I've never implemented it because its a lot of work for a little bit of trolling.
I thought here would be pretty vulnerable to it actually since people complain about being neg-rated so much(not that I would troll this place, I like this place), but I guess people (including me) figured out it was a bot extremely quickly.