"Anybody know what they mean? I was always under the impression planets didn’t emit light."

Well, planets certainly reflect light. And as Adam said they emit infrared- if the sunlight were blocked, planet would still emit infrared light.
Planets don't generate energy like stars do- transform matter [except radioactive decay]. But planets have energy- their orbital postion is potential energy, for instance the interaction between the Moon and Earth generates heat. Or an impactor hitting earth generates heat [very bright light, noise, and gnashing of teeth]. Or radioactive material is decaying [everywhere] and generating heat.
All planets would emit more energy than recieved from the Sun- because there simply more sources of energy other than the Sun- though at least at Earth distance, Sun energy dwarfs all other sources.