Update: Walker went back to his owner. He bit my boyfriends leg while we were out for a walk. He started growling at people when we past them, and I told myself I wouldn't keep him if he was aggressive toward people. He was such a sweetie, but I don't want to keep a dog that has that temperment.
On a good note, the owner is going to keep him, cause she doesn't want to take a chance with anyone else.