From the timing of the feedback, several weeks later, in all likelihood the buyer was prompted by eBay to leave feedback on their purchases. At this point, they though about the transaction and decided to leave the chosen feedback. The fact you refunded straight away, is probably the reason why the feedback was only neutral and not negative. Even if orders are cancelled, the buyer has always been able to leave feedback. As someone else stated, the buyer had no choice but to accept the refund at the time, it doesn't mean they were happy about it. We have all been in similar situations, just have to apologise and hope the buyer understands.