Fall blossoming in fruit trees (and other spring flowering trees and shrubs) can occur if the tree is stressed during the summer (heat, drought, etc.). While stressed, the tree may become dormant, and then when the weather moderates, if conditions are just right, the tree comes out of dormancy and flowers as if it were springtime. The trees do not usually expend all their blossom buds at this time, so there should be more flowers next spring, and hopefully fruit.

Spring flowering trees and shrubs form their flower buds in the late summer, so timing is a factor and the reason this does not happen every year. There was sufficient moisture as the buds formed, and then the environmental stresses induced dormancy, but the dormancy ended at a time when the temperatures appropriate for flowering occurred. There will not be time before frost for any fruit that formed to mature.

I would attribute this to our hot, dry summer and our very mild, warm fall. You can remove the blossoms if you wish. Keep the tree well watered throughout the rest of fall and the winter.