I am not sure what exactly you are meaning by predicting. You can tell the donor a different amount, than you are internally expecting to obtain.
The post concerns self-confirming predictions. The donor asked for a prediction of how much money they’ll give you...after they hear your prediction. A prediction you give them would be “self-confirming” if they gave you the amount you specified. Here “prediction” refers to “the amount you tell them”, as opposed to the amount
you are internally expecting to obtain.
which no one other than you actually knows.