Is there a difference between a hospitalist and an attending physician?

Not usually. A Hospitalist usually acts as an attending physician when you are under their care. However they can also be a consulting physician if you are in the hospital under the care of a physician of a different specialty like Surgery or Ob-Gyn. It all depends what your illness is and who is primarily treating you.
Attending physician. In a hospital setting, an attending physician is the quarterback of your in-hospital management. This doctor can be a Hospitalist, an office-based internist who also rounds in the hospital or even a specialist like a surgeon or Cardiologist.
Hospitalist. Hospitalists are specialized physicians who take care of inpatients. They may be internists for internal medicine patients, pediatrist for children and surgeons for surgical patients? They coordinate the care and upon discharge they contact the primary care physician and update the details. Not much of a difference.