The inputs of the model are full copies of copyrighted data, so the “amount used” is the entirety of the copyrighted work.
If you want to apply current copyright law to the inner working of artificial networks, you run into the problem that it doesn't work on humans either.
A human remembering copyrighted works, be it memorization or regular memory, similarly is creating a copy of that copyighted work in their brain somewhere.
There is no law criminalizing the knowledge or inspiration a human obtains from consuming media they did not have the rights to consume. (In many places it isn't even illegal to aquire and consume media you don't have rights to, only to provide it to others without those rights)
Criminalizing knowledge, or brains containing knowledge, can't possibly be a good idea, and I think neural nets are too close to the function of the brain to apply current regulation to one but not the other. You would at minimum need laws explicitly specifying to only apply to digital neural nets or something similar, and it apears this page is trying to work in existing regulation. (If we do create law only applying to digital neural nets, and we ever create intelligent enough ai it could deservedly be called a person, then I'm sure that ai wouldn't be greatly happy about weird discriminatory regulation applying to only its brain but not that of all the other people on this planet.)
A neural net is working too similarly to the human brain to call the neural net a copy but the human brain "learning, memorization, inspiration". If you wanna avoid criminalizing thoughts, I don't see a way to make the arguments this website makes.