At lower frequencies, the magnet or coil moves slowly so the output signal is small, while at higher frequencies it moves more quickly and so the output signal is disproportionately large – hence the need for equalization.
I was under the impression that the EQ was set on the cutting lathe to limit the physical excursion of the needle and thus get more recording time in the disc. Surely the EQ for playback will be exactly the same on the optical cartridge as a MM or MC cartridge.
Still interesting though.
Edit. After looking at their website and watching the manufacture I thought again. It seems logical that the optical conversion process is more linear than the induction process. With an output of 40mV it’s never going to work through a conventional phono stage anyway.