upper backs of male vs. females

quick question, in Charlie’s book, he has his female sprinters do behind-the-neck pulldowns, while he has the guys doing behind-the-neck presses.

why the difference?

No difference. Both did both. (careful with the behind the neck pull downs though).

i heard behind the neck press are bad for your rotator cuffs? is that true?

It can be safe if you:
1: Don’t use too much weight.
2: Don’t jerk the weight
3: Don’t let the arms extend fully at the top on each rep
If you want to go heavier, use a front pulldown with a narrow grip and stay with 2 and 3.