Smokey look on wood cabinets

Just tell people it is an expensive custom finish. Similar to the "distressed look" cabinetry. ;)

campfire smoke.

Or it could be soot from a furnace or kitchen stove that the flame isn't burning right . If it really is smoky looking. Windex does a great job on that.

May be moisture from the air. If you live where the Humility is High you may have to sand and shellac them.

Try a little furniture cleaner and see if that will remove it. Sometimes when an RV is stored closed up in a hot climate a combination of dust and heat will cause a layer of crud to be deposited on the hard surfaces.