Means that's the first person who tagged it as a 5 cow post. Some of the more recent 5 cow posts can be found here: http://forums.creativecow.net/tags/
lol... yeh, but what is a 5 tag post? I have a five tag post on my profile which is me basically asking someone else a question... and he never replied...?
Well... sometimes you get the oddball who marks a post as 5 stars for no apparent reason. Maybe he thought your attempt to draw the problem out of him was a good thing, who knows.