[yk]

The article uses 'shadow' in the sense of: region of less light behind an object. But actually, at this small scales the wave nature of light becomes quite important, since for an object smaller than the wavelength the distortion of the light wave is damped exponentially on an scale of the wavelength. So I think the word shadow is as appropriate as silhouette, since both somehow imply light rays ( and are therefore a rather loose usage on the meaning of the words).