Yes it is misleading indeed. From the description, the program extrapolated the emotional responses collected from 100 people for 500 paintings (??) to other paintings. No explanation is involved here to justify the use of "why" in the title as you point out. The title is likely to have made the original authors cringe.

Also consider this - the predictive power is dependent on the features tracked by the machine vision algo, which is decided by humans in the first place. We can ask whether the prediction would be as good as 80% if the vision algo only processed monochrome images. So was the "explanation" baked in beforehand?