Your son needed to contact Airbnb to cancel the reservation and arrange for a refund. You don't just take a host's word for it that they will send you a refund. That isn't how Airbnb works. A refund can't be issued if the reservation isn't cancelled.
There are many articles on the Airbnb site Help section for guests that explain how to do things like this. It's important for guests to inform themselves of how Airbnb works before they simply start making bookings.
@Tong58