If before posting, the buyer asked to cancel, why didn't you cancel which would have refunded buyer.
If you did not refund at thst stsge, then buyer is entitled to open a not received case, and you then have 3 days to refund, before he can ask ebay to take over.
The fact that there is an error in the description does not have sny bearing on the sale,buyer wants a refund.
If you have already refunded, money goes back to source and time taken is determined by method of payment, credit card can take up to 30 days.