Sometimes it pays to think before you speak. The DMV person was giving you a break as in California ALL pickups have to pay for commercial plates regardless of their GVWR or use, EXCEPT if you have a permanently mounted camper. When I spoke to several DMV employees I was told that the camper had to be welded in place and having turnbuckles would disqualify the truck as the camper could be removed.
Even a mini-truck owner has to pay the premium imposed by our legislature as a way to increase revenues. It is the old trick of cutting taxes on the rich while hitting the working stiffs with new fees.