Did OEMs wet sand and buff paint?

No unless they had a huge blem, orange peal is common on new cars.
What you see on cars with original paint, the weather, waxing have smoothed the finish down.

Go to your local car dealership and look at a new black car, it will have noticeable orange peal.

So they shot it with single stage and that was that?
No clear, no cut, no buff?

Not all that bad a result considering the method.