Reflection can't be brighter than the actual object itself, that's right, but what part of the environment is reflected directly from the object and what is reflected as a secondary reflection, is not necessarily the same thing. Highlight from the sun, or other bright light source can be invisible on the object, because its curvature, but when that same object is reflected in another surface, the highlight may appear visible and it may look that the object became brighter. It's simply optics. Corona does not invent things and it is physically accurate, Corona materials are written with energy conservation in mind, so you can be assure that they don't break physics laws.