In this experiment, I took at picture of an old photographic Kodak Gray Scale target with my Nikon D810.
I metered the exposure manually on patch M, which is closest to an 18% reflectance middle gray.
Here is RawDigger main window (with the cursor sitting on the M patch) :
And here is the Histogram window from a Selection of just the gray scale :
As can be seen, in this case, RawDigger did not use the Red channel value (about 794) to use for EV0.