@Violet3 It seems that this action by Air BNB was against policy unless there were extenuation circumstances causing the cancellation. Or, if the guest submitted a reservation change and it was accepted. I gather neither happened, right?
Please not that your strict policy says: If the guest arrives and decides to leave early, the nights not spent are not refunded - the seven days is for before the check in and the guest can get 50% refunded. https://www.airbnb.com/home/cancellation_policies#strict