I've seen this kind of thing happen before, and I don't think it's a question of demographics or sockpuppets. Basically I think a bunch of people upvoted it because they thought it was funny, then after there were more comments, other people more thoughtfully downvoted it because they saw (especially after reading more of the comments) that it was a bad idea.

So my theory it was a question of difference in timing and in whether or not other people had already commented.