Alright, honest mistake. Like I said it's a gamble, so you don't have to refund unless you feel like it. In the future though, blockexplorer will show you where you've received bitcoins from, like
here.
The actual bitcoin client is pretty bad at showing where you've received a transaction from, I don't think I've ever seen a transaction come into my wallet that the client was able to tell me where it had come from. (That is to say, it displays the same "unknown" text that you saw.)