Not enough information Kumquat to give the best answer here - a photo of the tree and fruit and the location of the tree would help. (Does your son live in North Florida too?)

A few things to consider:

Persimmons normally do have a June drop that can continue into early July, and the fruitlets often discolor prior to falling, though they usually turn brown rather than black. Your son may ask the neighbors whether the tree usually produces edible fruit in previous years.

Knowing whether the tree is an Asian or an American persimmon can make a difference in determining what's going on and what to do about it. You say it's a big tree - those over 30 feet tall are usually American persimmons. The leaves of the two species are different and can fairly easily distinguish between them - you can compare the leaves to on-line photos to make the ID.

Abnormal fruit drop may be from too much or too little water, excessive nitrogen applications, excessive heat, lack of pollination (in certain varieties)and disease. Leaf discoloration (especially blackening), disfigurement or loss together with fruit drop suggests an infectious process.

He lives in Santa Rosa Beach. Sandy, acid soil. Hotter than the hinges of hell. No rain for over a month. It has started raining now. Tree is 15 feet tall.

I am seeing black on flowers that are starting to grow fruit. Not sure if it is the same problem you have. They fall off if touched or looked at wrong. Meader American persimmon.

Probably not pollinated