Given his track record—which is roughly estimated by his karma score—I would assume a lot of things before I assumed that Yvain had genuinely posted something that impressively stupid. (Hacker, friend at keys, misunderstanding, etc.) So I probably wouldn’t vote on it, but if followup comments made it clear that yes, it was Yvain, and yes, it was really that stupid, I’d downvote the followup.
Given his track record—which is roughly estimated by his karma score—I would assume a lot of things before I assumed that Yvain had genuinely posted something that impressively stupid. (Hacker, friend at keys, misunderstanding, etc.) So I probably wouldn’t vote on it, but if followup comments made it clear that yes, it was Yvain, and yes, it was really that stupid, I’d downvote the followup.