I think he means if PFD screen is off (PFD showing on ND screen) pushing XFR will show the ND, hence no PFD on either screen.
FCOM DSC-31-50
PFD BRIGHTNESS CONTROL KNOB
Rotating this knob all the way counterclockwise switches off the PFD. In this case, the PFD image is automatically displayed on the NDU, but the pilot may recover the ND by means of the PFD-ND XFR pushbutton
So yes, they will still transfer if PFD is off