The only conclusion I can draw from the response is that it was a shill bidder or somehow connected with the seller. Most would either ask you questions as to why you think it's fake or ignore you completely. They won't write profanities.
Ugh, I hate shill bidding! I have been in a situation where I saw a particular id bidding it up so much, so I suspected of shill bidding and stopped. That bidder won and I kept my tab on that transaction and sure enough, there was no feedback left for either party.