There are fundamentally two alternatives to specifying "who looks European".

Alternative #1 is to have an a priori definition of what "a European looks like". Individuals are judged against this definition, and those who don't match it are deemed "non-European looking".

Alternative #2 is to consider how Europeans actually look like. By establishing the range of variation found in native Europeans, we can subsequently determine whether an individual belongs within that range of variation, and hence, whether the "look European" or not.

The relative value of the two approaches can be determined by their success in making correct inferences based on partial information. Those who followed the a priori approach -predictably- failed to correctly infer the person's ancestry. Those who tried to match the person's appearance with their knowledge of European variation made the correct inference.