I think you will find that my description of the interaction of radiation with matter is in line with contemporary quantum theory. In the kinetic theory of gases, the temperature of a gas is defined as the average kinetic energy of the particles making up that gas. The atoms and molecules in the thermosphere being at a high temperature consists in the fact that they're travelling at high velocities. The only opportunities these particles have to convert their kinetic energy to radiative energy occur during collisions with other particles, which are rare due to their long mean free paths. You have formed the impression that the solar radiation in the thermosphere is particularly intense. But we can actually measure the intensity of solar radiation at the top of the atmosphere, where it's about 1.36 kW/m2, and compare it with the intensity of the solar radiation on the Earth's surface, where at midday it's about 1 kW/m2. (The Wikipedia article on "Solar Constant" is an accessible source for this.) That's not that big a difference, so it would be surprising if the radiative equilibrium temperature of a black body at the top of the atmosphere were much different than the equilibrium temperature of the same body at the Earth's surface. It would be interesting if you could answer Trailblazer's question about what makes the thermosphere special. Would you agree that the solar flux in the thermosphere is about the same as it is on the surface of the Moon, for example? If you think it's significantly higher, what do you suppose causes that?