Hi @Maureen79
Unfortunately it sounds like you have fallen into the trap that we see quite often on these forums, and not read through how cancellations work with Airbnb before doing this. Have a look at Airbnb's Help Centre - host cancellations and you will see the impact of cancelling as a host.
There is no reason you guest couldn't have cancelled the booking. All they had to do was go into their booking at hit the CANCEL button on their booking.
Give Airbnb a call now. They should be able to see through Airbnb messaging that your guest wanted to cancel the booking. Ask them if they can set this as a guest cancellation.