Funnily enough, while the thermosphere is technically extremely hot, any solid object put there will tend to get very cold on any surface that isn’t in direct sun. “Temperature” is simply a measure of the average kinetic energy of the molecules in a substance. Yes, the gas molecules in the thermosphere are moving very fast (hence the high temperature), but the pressure there (that is, the number of gas molecules in a given volume) is extremely low - basically a vacuum. The upshot is that solid surfaces lose heat by radiation of infrared to space far faster than they pick it up from the “hot” thermosphere. So, they cool down.
