We could use "Writing a Sonnet" as a suitably discrete and limited form of art that's undeniably art, and ask the question "Can a computer creatively write a sonnet"? Which raises the question "Do humans creatively write sonnets?" or are they all derivative?

Humans used to think of chess as an art and speak of "creativity" in chess, by which they meant the expression of a new idea on how to play. This is a reasonable definition, and going by it, chess programs are undeniably creative. Yet for whatever reason, the word doesn't sit right when talking about these programs.

I suspect we'll continue to not find any fundamental difference between what the machines are doing and what we are doing. Then unavoidably we'll either have to concede that the machines are "creative" or we are not.