Looks like the speed climber turned back about 100 meters from the summit because he was afraid of his toes being too cold. If he had wanted to breathe supplemental oxygen, he probably would’ve made it. But, as he says, if he had used oxygen, he would have been on the summit of a different peak. Read his whole story here.
“The adventure [at] Everest is over. Pity, I was doing well. I imagined that I would only suffer up there. Not at all. I am happy about that. I had a great feeling, I moved on, that’s what I am looking for, although I turned back 100 meters from summit. Of course I would have been nice to stand on top. For a moment I have thought to ask a Sherpa if I could breathe 10 minutes of oxygen. Then I would have had again warm feet. But then I would have stood on another peak. So better to go down. Everest will stay and I can come back!”