So, you see, the actual radiative temperature in the thermosphere is DEFINED as upwards of 2500 C because of the heat of the sun. It is NOT a temperature that is merely expressed due to translational kinetic energy of a single particle due to the lack of surrounding mass, nor is it defined as 'not really actually hot because there's not that much stuff up there'. It is actually, really, no really guys I mean actually really hot!
You are quoting from a site called "study.com" that appears to be not very rigorous (to put it kindly). The passage you quote is full of errors.
Take this excerpt:
Since there is little to no atmospheric gases above the thermosphere, there is no absorption of the heat from solar radiation, and so temperatures soar.
Not only does this directly contradict the Wikipedia page that you quoted just above it, which states "Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation
", but a moment's consideration will tell you that it is nonsense.
If there is "no absorption of the heat from solar radiation", then how can "temperatures soar"? To make things hot, they have to absorb heat energy. And anyway, temperatures of WHAT? Electromagnetic radiation (such as sunlight) in and of itself does not have a "temperature". You can talk about the effective black-body temperature of radiation, which is the temperature a black body would have to have in order to emit the same radiation spectrum, but this is not a measure of temperature as we know it.
For example, sunlight has a black-body temperature ("colour temperature") of about 5,800 kelvin, or 10,000 degrees Fahrenheit. Does that mean sunlight will heat you up to that temperature if you stand in it? Of course not.
You may recognise the term "colour temperature" from the packaging of lightbulbs:
Notice that a "cool white", or daylight, fluorescent bulb has a colour temperature almost the same as the sun (that is what it is designed to mimic). That doesn't mean it will heat you up to 10,000 degrees Fahrenheit if you stand under it! The monitor you are looking at now probably has a colour temperature higher than that of the sun, maybe 6500 kelvin. How are your eyes coping with that searing radiation?
So, you see, the actual radiative temperature in the thermosphere is DEFINED as upwards of 2500 C because of the heat of the sun.
No it isn't. There is no such thing as "the radiative temperature" unless you define what you are measuring the radiative temperature of!
If you put a piece of shiny aluminium in the thermosphere, it will have a radiative temperature somewhere below zero Celsius. If you put a matt black painted piece of plastic there it will probably be somewhat higher. If you put a helium or oxygen atom up there and it gets zapped by an X-ray and ionised, then it may attain a temperature of a couple of thousand degrees Celsius because it will go whizzing off at high speed until it eventually hits something. If the same X-ray strikes an atom in the hull of a spaceship then it might knock an electron loose, the energy will quickly be absorbed by the other neighbouring atoms, the electron will find a new home, the heat will be re-radiated back into space, and not much else will happen.
Space doesn't have a temperature*. Radiation doesn't have a temperature. Physical objects have a temperature, that depends greatly on their properties.
I am still at a loss to understand why you think the thermosphere is a special extra-hot place. What makes the solar radiation in the thermosphere so much stronger than, say, the solar radiation on the moon, or out in deep space? The sun only puts out a certain amount of energy. If it could heat stuff up to 2500C in the thermosphere then surely the Earth and the moon ought to be glowing white hot as well, after all they're at a similar distance from the sun, right?
* well, unless you count the cosmic microwave background radiation, but that's less than minus 270 Celsius, so astronauts are still going to need to pack thermals.