@Daniel1127 You are saying two contradictory things. "The guest booked and I caught an issue on my calendar so I canceled his reservation and I was polite enough to ask him to cancel it and he agreed."
What do you mean you were kind enough to ask him to cancel it? Did the guest cancel or did you? It appears that you cancelled- just because the guest didn't make a fuss over it doesn't mean it doesn't count as a host cancellation. If your calendar isn't up to date, that is your responsibility as a host, not the guest's issue. It isn't kind at all to cancel a reservation.
Hosts recieve penalties for cancelling bookings. Exactly to discourage hosts from doing so. A fine is one of the penalties (Airbnb keeps that money, it doesn't go to the guest) Your calendar will also be permanently blocked for the dates you cancelled, so you can't rebook them, and a message will be put in your review page saying "Host cancelled this booking XX days before arrival", which can make future guests reluctant to book with you.
You really should inform yourself of Airbnb policies, so you aren't taken by surprise. For someone who has 333 reviews, I'm astounded you were unaware of the cancellation penalties.