You got me excited thinking eBay had returned to equal feedback for buyers and sellers!
I think you can report it if it's a negative comment on a positive. You can also ask the seller to revise it since they've been completely unreasonable. Or put a comment on it saying 'feedback left after two days and a pestering email from seller'.
I wouldn't worry about it , it will still be a positive on your feedback , some people are nutters , think this was prob one of the reasons they stopped sellers leaving anything but positive feedback on buyers !
Ebay is the province of the barking. If it really bothers you, you can leave a follow up comment and or report it as negative comments aren't supposed to be left with a positive rating but personally I'd just let it slip off the page.