Definitely go back to the DMV. We're going to assume your vehicle is a Heavy-Duty truck. It is no uncommon for heavy duty vehicles (and engines) to have the Federal Emissions Label affixed to the engine block. The DMV agent may have been unaware of this fact.
Unless this truck has had an "engine change" (an engine change is considered an engine replacement with that of another make, model, or year) you should not need a Referee Smog Inspection. Then again, the DMV is the ultimate decision maker when referring vehicle's to CHP or Referee inspections. If they have found other reasons to require these inspection you'll more than likely need to adhere.
