Setting a correct user agent isn't required anyway, you just do it to not be an asshole. Robots.txt is an optional standard.

The article is just calling Perplexity out for some asshole behavior, it's not that complicated

It's clear they know they're engaging in poor behavior too, they could've documented some alternative UA for user-initiated requests instead of spoofing Chrome. Folks who trust them could've then blocked the training UA but allowed the alternative