Plates are run automatically now with cameras. If that is legal, and I think the courts have ruled it is, the stop was legal and justified for the non match on the plate.
Mmmm...have to chew on that one for awhile. You are right about automatic tag checks by camera, but they are only compared to a very specific hot list of stolen tags or vehicles or wanted persons associated with the vehicle. But something to chew on...
The courts have ruled that 0bamacare is legal ... among other atrocities.