In some use cases this OnAdFullScreenContentClosed event is ambiguous.
You don't want to give user reward when he skip the ad and there's no way other than OnAdFullScreenContentClosed to know if user skip the ad or not.
And on the other way OnAdFullScreenContentClosed also call on ad watched completely and closed.
So you can't add logic of not rewarding the user in case of skip the ad in OnAdFullScreenContentClosed event.
Hopefully you understand my point.
Thanks