Dear Railiung,
For cylinders, “yes,” the chord is equivalent to the diameter.
You can consider the cylinder data and diameter/chord at the root of the NREL 5-MW turbine as approximations chosen to give reasonable aerodynamic loads within aero-elastic simulations, but not necessarily exact specifications for creating a solid model of the blade. For example, it has been pointed out the root diameter is larger than the hub diameter for the NREL 5-MW turbine, which is obviously unrealistic–see the following forum topic: NREL 5 MW Hub Radius.
Best regards,