This was my first thought too... You can already see in the examples in the article that the model understands that photos of people tend to have reflections of

This was my first thought too... You can already see in the examples in the article that the model understands that photos of people tend to have reflections of lights in their eyes. It understands that both eyes tend to reflect the same number of lights. It's already modelling that there's a similarity relationship between these areas of the image (nobody has dichromia in these pictures). I can remember when it was hard for image generators to model the 3d shape of a table, now they can very easily display 4 very convincing legs. I don't have technical expertise here but it just seems like a natural starting point to assume that this reflection thing is a transient shortcomimg.