The thing is, that one word is a pretty vital word. It's not a Leatherman and shouldn't have been called that. It doesn't matter what the photos show, both your title and miniscule description both say it was a Leatherman and it's not. I wouldn't have been happy either. I probably wouldn't have left you bad feedback, but it's the buyers perogative to do that as they weren't happy. 

The rest of your feedback is good. You won't be able to get that feedback removed, so the best thing to do is reply, apologising for the error in the listing and that you take full responsibility. It shows other buyers that you will own up if you make a mistake and you won't abuse them like plenty do.