After calibration is finished, dispcal scales and then applies the VideoLUT values it generated.
I think there may be a misunderstanding. Dispcal does not apply the calibration it generates. It resets (to linear) any video LUT curves that might be present before starting measurements, and thereafter, it restores them. So when invoking dispread, to actually use the calibration you created, you have to provide the -k parameter with the cal file as argument (or invoke dispwin file.cal first, but using the -k parameter is clearer). Otherwise dispread measures the display in whatever state it happens to be in. All mentioned in the Argyll docs btw :)
Regards, Florian Höch