The stimulus tells us that art is pleasing if the viewer gets the impression that the arranger succeeded. In A, people do get the impression that the arranger succeeded, despite an error. A then concluded that the panels should be rearranged to reflect the intention. However, we do not care about the artist's actual intent, only the impression that the artist achieved their goal.
D, however, only relates to the appearance that the artist got what she wanted. The idea that pleasingness is related to the impression of intentionality does support the idea that a more symmetrical arrangement would be more pleasing, since it would seem more intentional.