If a human can learn from existing art and information, how is that different from an AI learning on the same? Or replace AI with a new sentient being that is discovered.

What one does with the learning seems to be the issue. If a human exactly reproduced anothers' artwork, that'd be copying.

Yes and actual artists acknowledge copies. Art is a craft and if the copy is well made by actual human skill you can value it. AI artists act like printing out the Mona Lisa is their own art, skill and expression.