APPEARS to cast light, because the light falls in the appropriate area. But it isn't luminous in the way a genuine light source is.
Then what's your metric for determining what is and isn't luminous in a "genuine" way? If it's not the luminosity and it's not the exposure and it's not whether it casts light on something, then what is it?
By the way, as someone who does work with CG objects, the illumination on the Abramsprise from the windows looks like Final Gather-type rays cast from the incandescent geometry. As far as is possible for a virtual environment, that would make it real, actual illumination.