That's what I'd like to know. His feedback comment is "very good , thanks." On a 1 cent auction, no less. I submitted a revision request and all that, but I doubt he's going to change it.
That sucks, but it sounds like it was a mistake. The guy probably clicked on the negative button by mistake. Contact him and ask him if he really meant to leave a negative feedback. If he says that it was a mistake, ask him to leave a note under his feedback explaining that it was a mistake.
If he does that, then the worst case scenario is that any potential buyers who read that feedback will know that it was an accident. Best case scenario, you might be able to contact ebay and have them change it to a positive feedback.