This paper isn’t saying that it doesn’t matter what program you do, it’s saying that other variables, not directly related to the method of weight training, matter more. It also assumes that you can extrapolate data from one individual training each limb with a different program to if that individual performs either program on both limbs. Maybe there are carryover affects to the lower load limb that you get from training heavier with the higher load limb that you wouldn’t from training both at a lower intensity.