If you look at the info graphics at KS page about brain warp you notice that it means rendering frames for left and right eye in "leapfrogging" fashion. The frame rates visible by each eye remain the same, the time point however are shifted for T/2 (where T is 1/F, F is refresh rate).
To give an example:
t=0, left eye is rendered
t=T/2, right eye is rendered
t=T, left eye is rendered
t=T+T/2, right eye is rendered
Refresh rate observed by left eye is 1/(T-0) = 1/T = F
Refresh rate observed by right eye is 1/(T+T/2-T/2) = 1/T = F
Which means F per eye.
Now from the global system perspective, the displayed information changes, twice as fast, because the left and right eyes are interleaved. So we can say the overall system refresh rate is 1/(T/2) = 2*F.
If you assign F=75 Hz per eye, you get overall refresh rate 2*75=150 Hz, for F=90 Hz, you get overall refresh rate 180 Hz.
So far it is just playing with numbers, to explain "per eye" and "with brainwarp". It does not explain whether brain warp is actually good for anything or not (I have my doubts). On the other hand, what Pimax wrote in the line you quoted and what they showed in the info graphics is technically coherent and correct. You do not need to make it more complex and convoluted by trying to relate it to Pimax 4K headset tech, which is clearly quite different.