It's possible especially since he was abused as a pup.
But at the same time, usually puppies love
everyone.
It is when they start maturing to adolescent stage their
personality will usually change.
I think positive training and even an evaluation from
a behaviorist could not hurt.
(Also to I am assuming your dog is healthy,
because when they are not feeling well they
can act irritable too.)
GSD can be protective and loving with
family members but not that way outside of the family.
Not every dog likes strangers.
But the family dog should be tolerant of family
members.
(I did not know what a ACD was)