He's all over the place in this video. He says the Mac Pro CPU is 3.3Ghz, but it's 3.7 in the description, says he has D500s but it says D300s in the description, and doesn't mention the size of the SSD.
The machine he mentions in the description is only $3,000, not $4,000. It's also from 3 years ago (if you count the GPUs, up to 5) so for the time, $3,000 is actually fairly reasonable (although not any more). So his point is a bit muddled. If you bought this machine now, it's a little overpriced, but at the time it was a good deal. You couldn't spec a machine to the same level for the same price back in 2013.
The title of the video is deliberately sensationalist so as to be clickbait.
He might as well get an original Macintosh and say "Oh look, I've just built a PC for less than this retailed at back in the 1980s and it's waay faster". Yes, it would be. It's 2016..