This is a common excuse, but it's not actually true, and also not how copyright law works. Whether a use is educational is not the primary determiner of whether something is fair use - it's whether or not the use affected the commercial viability of the thing being copied.
The reason that humans learning from artwork can be found fair use under copyright law is because humans learning to draw from other humans has not been shown to affect commercial viability of the original work. This is because human artistic output tends to be rate-limited, and there aren't that many humans who learn to create art in a particular style regardless.
While originality and educational use are both things that might help establish fair use in the absence of a market effect, if there is a demonstrable market effect it is very hard to show fair use. This is likely to be the case with AI art, since machines can generate a lot more art (not to mention copying a lot more exactly), and they are in fact marketed as being replacements for human artists.
In summary, at least in this particular sense, copyright law already correctly accounted for the difference between humans and machines, even though that wasn't specifically something it was designed to deal with.
No. All information is stolen from somewhere else. There is no such thing as originality. If Miyazaki gets paid then he should be paying all of the people that trained his brain too.