That shouldn't even matter. They provided me a bitcoin address, and I paid with bitcoin. I don't care if their payment processor converted it to dollars or not; not my concern. Once the bitcoin leaves my wallet and hits the address that their website or rep provided, that's that. Everything else is an irrelevant internal detail.
If you paid in dollars and they claimed that they don't owe you a dollar refund because they quickly bought a few bushels of coffee beans with your payment, and you're therefore only entitled to refund in coffee beans, would that make sense?
Until a judge rules on this, we can only speculate. I do see both sides of the argument, but frankly, I do think HF have a case here. AFAIK, their products were priced in dollar, not bitcoins. Bitcoins were used to fulfill the dollar amount but the number of bitcoins needed to fulfill that amount would have changed daily. Did you think that was unfair too? Its clear to me this wasnt a barter trade.
Another way to look at it; if you had paid with a bank cheque; would you expect or demand to get that very same paper cheque back? Or just the equivalent dollar amount since that cheque was just a way to supply HF with the dollars it demanded for their product? Maybe that bank cheque was signed by a bank director that became a presidential candidate or whatever, and has become worth much more in the mean time, but thats not HF's problem, or is it?
The details of what happened are not in question here. The issue at hand is HashFast agreeing to refund cancelled orders with BTC, and then refusing to honor that agreement. Simon Barber (Founder of HashFast) was asked by cycloid on the 10th of August 2013 if refunds would be in BTC.
He clearly asked in this post
https://bitcointalk.org/index.php?topic=270384.msg2903196#msg2903196"Now since the only payment option is in BTC Will I get the same ammount of BTC back should you fail to deliver by December 31st?"
"Or are you going to pull BFL and give refunds at exchange equivalent to USD/BTC indexed to the current fiat price per unit?"
Simon Barber's (HashFast's) official response was
https://bitcointalk.org/index.php?topic=270384.msg2903338#msg2903338"Orders are taken in BTC, in the unlikely event we get to refunds they will be given in BTC."
Perhaps you do not 'see both sides of the argument'. Both parties entered into an agreement, that agreement was conditional on the refund being in BTC. It is starting to look more like a clear case of fraud.