Yes, in case someone gets a painting without any additional information, a computer art piece, could easily be mistaken for a human art piece. That's true. My position on the subject is as follows, the best art for humans is made by humans, and the best art for computers is made by computers. Actually i have yet to see a computer generation on the same level as Mona Lisa, not even close. However computer generated women, some of them are alright!
But the definition of art can't depend on your knowledge of how was it made. I can show you two beautiful pictures and ask you if any of them is art, and you'd know I was trying to trick you. But you could pass a piece made by an AI as art if you didn't know how it was produced.