@Hillary1 Hi Hillary, Although you are an experienced host Airbnb have recently changed the format of their cancellation options and although you may have felt that the cancellation was the guests action, through contact with Airbnb you probably cancelled on behalf of the guest and that now renders you responsible, and it now shows as a host cancellation.
This question has been raised a number of times over the past couple of months and I am sure the rest of us would appreciate a bit of follow-up on this. Plead your case to Airbnb and see if this notice can be overturned and I would ask that you keep the community informed as to the outcome.
Good luck Hillary....cheers......Rob