It's semantics.
QNH is measured, in principle with an altimeter, at the aerodrome level, by looking at the subscale setting that causes the altimeter to show the aerodrome elevation. It doesn't need to be corrected for temperature, save for the correction for error in the instrument itself, which is likely to be very small.
As soon as you move above or below the level of the aerodrome, temperature errors creep into the indicated altitude, as the altimeter is calibrated to the ISA. If you move from an aerodrome at a considerable elevation down to sea level, you may find that the indicated altitude is not zero. Similarly, if you measure QNH at a sea level reference (Sea Level Pressure) and use it at your high aerodrome, you may find it to be incorrect. In that sense aerodrome QNH is sea level pressure "corrected" for temperature.
And any time you use a QNH at a level different from the level it was measured at, you may need to apply a temperature correction. In particular, in IAPs in cold conditions, the altimeter will overread so a correction for temperature is required at any altitude that is critical.
chevvron, are you sure that's not the conversion from QNH to QFF (Sea Level Pressure)?