It's the latter: An "upright face" is a face that has its chin below the forehead. For our eyes, those look like upright faces, but in Claudio's eyes they look

It's the latter: An "upright face" is a face that has its chin below the forehead. For our eyes, those look like upright faces, but in Claudio's eyes they look like what inverted faces look to us. So, because Claudio is not better at detecting upright faces than inverted faces, even though most of the faces in his life have been upright, that suggests an evolutionary component.