As a 10/10er, I think the fact that people tend to score less goes to show that:

1. The photos are low-res enough to hide the most ridiculous artifacts produced by neural nets

2. The machine-generated images are trying to emulate the likes of van Gogh, not the likes of Leonardo (again hiding the extent of NNs complete inability to understand what they're doing)

3. Most people simply neither paint nor appreciate visual art, so this is not as powerful as the Turing test! (One point of the Turing test is that a human easily passes it, because all humans speak; they don't all paint.)