They likely didn't account for edge diffraction, atmospheric light scatter, and room reflections.
When the flamethrower first turned on, I was surprised at the lack of light created by the flame. The reflections look good, but the fire didn't emit as much light and cast shadows as I expected.
It's a nice new feature, but just one of many - and still in it's infancy. Not worth an upgrade from my 1080ti on RT alone.