The difference is that when a human creates Picasso inspired art they're creating it with the summation of all their life experiences. However, an AI trained only on Picasso, knows nothing of Picasso. It's a subset of his knowledge and can't add anything new. It doesn't know anything about art that Picasso didn't know. If you scale this up it's still true. An AI trained on many works of art doesn't know anything about art outside of the art that was put into it. It's the equivalent of a human living it's entire life in a pitch black room with only paintings of Picasso illuminated.