You would be smart to always have him on a leash when outside or around other dogs and if he were mine I would put a muzzle on him so he can't bite anyone. Then I would work with that trainer and do everything I could to get him trained. He is still very young you would think there is a lot of room to work on training.
Athena -GSD- born 12/13/12
Luna -Shepherd Mix- born 3/20/99