Wheel modifications apply to both Stock and Pro Stock Classes. In the case of the term "lightened wheels", I'll agree it is an ambiguous in contrast to reducing wheel diameter, coning hubs, or trueing treads. Of course, a wheel that has had any material taken off will be lighter than out of the box. The term in the diagram refers to more than just adjusting for a true and perpendicular wheel. It is mean to restrict large amounts of material to be removed where the wheel is substantially lighter that an out of the box wheel.
So for Stock and Pro Stock, you can lightly sand the outer tread, cone the hub, true the tread, or lathe the outer tread reducing the diameter to no less than 1.170 inches. That's about 0.015 inches less than a standard out of the box wheel. No inner lathing or removal of material from the inside of the wheel or tread is allowed.