While Yates did low volume, as Thate said, his intensity was the key. He regularly made use of forced reps, negatives and rest pause. Yates's rep ranges was 6-8 for upperbody and 10-12 for legs....he stated he grew best with that range. Many dont realize that Yates did do feel-sets/warmup sets on his heavy, compound movements...although he still tore muscles as mrhtbd stated due to going heavy always. However, Yates usually only talked about his "work sets", so people misconstrued his work sets for total sets...big difference.
Example...Yates on incline barbell: 135 x 15, 225 x 8, 315 x 8, 405 x 6...his last set with 405 was the only set that he busted ass on, hence, 1 WORKSET...the only set that you HEAR about. But notice how he pyramidded up. Its important to realize that, as many have the wrong idea and thinks he just did 1 warmup set even on the heavy basics and then boom, go heavy...NOT. Thats an easy way to get hurt!
Actually, Yates whole scheme was nothing really so unorthodox when you factor in the TOTAL sets he did and not just the work-sets. He just busted ass harder than most, did less and rested more. Heres another example that shows how the average Joe can be misled and end up getting injured due to naive ignorance:
Yates chest day:
incline bb press: 15, 8, 8, 6*
flat hammer strength press: 10, 6*
incline db flyes: 10, 8*
cable crossovers: 10*
* = worksets
You see the WORKSETS there is only 4(the sets you hear about

)...however, TOTAL sets is 9. People only discussed Yates worksets, so the average Joe might think "WOW I do 4 sets only"...SO Joe knocks out ONLY 1 warmup set with 135 on incline then jumps right to 315 and BOOM...popped pec...nigga didnt warmup enuff as he had set in his brain "4 sets". So its very important to distinguish and acknowledge that Yates DID do warmup/feel-sets.
Hope that helps