I did 20 rep squats a year ago several weeks in a row, and my last week was 365. Couldn't find the video, but this was my 345.
Regardless, I'm saying this because I know EXACTLY what this is like.
20 rep heavy squats are one of the absolute most taxing things I've ever done in lifting. They were hell. When I did these, I was already back squatting weekly, and in reasonably good condition. I can't imagine going into this the way he did after not back squatting for 3 years, as he indicated in the video. I'm definitely impressed. I'll also say that the way he did this is indeed more difficult than my set. Holding the bar on your back that fucking long takes a serious toll.