Could be several things. Many fruit trees often set more fruit that the tree can possibly support, dropping some eases the stress on the plant.
A sudden spike in heat can trigger fruit drop as can water stress. There are nutritional reasons for fruit drop but your tree sounds healthy. Poor pollination can also result in fruit drop.
Is there still a good amount of fruit on the tree?

Yes.There is still a good amount of fruit there.But I expect the crop to be higher than last year.Facts will prove. The caliper trunk size at base currently is about 4 feet.I doubt it is heat stress or water stress,this year the temps have been quite consistenly low compared to last year.In the spring we had good rain.This has been a great year for rain.Most reservoirs aroun here are full.
So I do not see reason for drought which causes stress.