Is a facial plastic surgeon different from a plastic surgeon?

The two titles sound interchangeable, and the boards behind them define them differently. This question belongs to the stage before choosing a surgeon.
The short answer
Yes, the credentials are defined differently. Each board describes its own scope, and the wording shows where they part.
What each board says
The American Board of Facial Plastic and Reconstructive Surgery describes its role as certifying surgeons exclusively in facial plastic and reconstructive surgery.
The American Board of Medical Specialties lists a subspecialty called plastic surgery within the head and neck. A plastic surgeon trained in this area has additional expertise in plastic and reconstructive procedures within the head, face, neck and associated structures, including head and neck cancer and reconstruction, management of maxillofacial trauma, soft tissue repair and neural surgery.
Checking the credential
Look up a surgeon's board status instead of trusting a title. The home page of the American Board of Facial Plastic and Reconstructive Surgery is one place to start, and the American College of Surgeons keeps a patient and family resources page.
What would change the answer
A title with no named board behind it is a reason to ask which board certified the surgeon. The name of the board tells you which of the two definitions above applies.
The question that usually follows
Readers next ask which credential suits the procedure they are considering. Put that to the surgeon directly at the consultation, and ask about training as well as the certificate on the wall.