Does Apple bill the developer for the value of the refund? Charge their credit card? Do they withhold future sales for that value?
Actually, I imagine this is just an oversight, and he's been caught in-between some automated cracks. If he raises the issue with Apple and it isn't resolved immediately, then it's time to grumble.
Like the developer says in his own Tweets: for that, there would have to be an open channel between developers and Apple. There isn't, developers don't get to discuss with the Apple App Store representatives, it's a one way dialog in which they receive some automated or if they are lucky, semi-automated response from the App Store and that's it.