Note that he said higher quality, and not better. There is a bit of a difference, as better could mean different things to different people.

You can find plenty of things about the (raw) denim subculture as far as Japan goes, this is probably a decent intro article: https://www.heddels.com/2013/06/what-makes-japanese-denim-so...

Note that none of these brands are really literal workwear. They're not competing at all with carhartt (Most of these pairs will run you $300 at least eg.), and almost everybody who buys a pair is going to buy them for the experience/authenticity and aesthetic (Americana)