Why is back radiation even relevant? It does not change the fact that energy can neither be created or destroyed.
However, after a warm summer day, I do know what it feels like to feel warm by walking past a building that is warm to the touch. And, there is a fact that infrared thermometers measure cold temperatures as well as hot temperatures and the fact that we can see stars that are cooler than the Sun, like Betelgeuse, in the night sky.
Back radiation exists because the Second Law of Thermodynamics is a statistical law and not a fundamental law that does not apply to subatomic particles. A black body will emit photons in all directions, without pointing a thermometer in the direction in which the photons are going. But, the warmer body is always the more effective emitter of photons, so more energy will travel from the hot body to the cold body than from the cold body to the warm body.
Do not believe biased sources like /principia-scientific.org without checking with reputable sources, like NASA and NOAA.