Basically, I think you got done over Marius. Surely any technical problems would have affected more than just the one auction and eBay would have been much more proactive in looking at a number of auctions - we'd have heard about it, in summary.

Latency and lag can be a problem, but if it's a persistent problem for someone, you can bet they wouldn't leave it to last-second sniping all the time. Nope, looks to me like the seller didn't like the end price and found a way out.

Unfortunately, eBay have the option of pre-approved bidders as a way of circumventing those off-eBay deals that are against the rules (and, of course, taking a fee from a sale they would otherwise have no interest in) :

Pre-Approve Bidders/Buyers
Allows select sellers of high-profile listings create a list of specific eBay members who are allowed to bid on or buy an item they are listing for sale. Each pre-approved list applies to only one item, so sellers can restrict bidding or buying on one listing without changing the other listings. Members not on the pre-approved list must email the seller for approval before they can bid on or buy an item.

It says "high-profile" but if it's anything like it used to be (been a while since I used my seller account), it could be used on any listing. So unfortunately I doubt eBay would pursue that private BIN.

It's a shame, the burden of proof over the technical issues should have been with the seller (and basically impossible to prove) and that's what eBay should have insisted on.