This is a longtime rumor that does not appear to be substantiated. But even if it were true, the amount of wolf blood in modern GSDs would be pretty negligable.
People have been experimenting with wolf/GSD crosses in an attempt to make some kind of super-working dog, but actually, they generally make lousy working dogs. If there were individual dogs in the early GSD that dipslayed wolf-type behavior or temperament, they were probably culled. It would have been totally counter to their breeding goals.