Yes in that case it's true. Besides the design of most CdS based meter do not use a logarithmic amplifier and thus even if the response of the CdS cell is fairly linear its output isn't linear to the EV readout. I have done some experiment by copying the design of some CdS meter and found that without such an amplifier (a circuit that only has resistors, a power source and a galvanometer) can be made linear to a range of about 7 or 8 stops. And then I would have to put neutral density in front of the cell to switch to higher range.