Darkoz doesn't think that only low reps will build muscle very well, despite literally hundreds of weightlifters with completely ripped quads, shoulders and traps as evidence to the contrary. Apparently you can be 5'10" 77kg and shredded, stick 379kg over your head in two lifts and not be jacked- simply because you didn't do more than 5 reps, a completely arbitrary round number (xiaojun). A decent part of Science and Practice of Strength Training will corroborate this, as will just about every strength athlete on earth
My guess is that might be the core of his training, but that is not ALL he has done. Other elements, gpp for example, have helped him get so ripped and shredded.