To transmit audio you have to encode it into electromagnetic radiation, transmit it and then decode it to reconstruct the audio.
You might have noticed that the audio transmitted on lower frequencies or longer wavelength sounds worse. AM (medium wave) sounds pretty bad, long wave sounds even worse. Even lower and you can’t make out speech anymore, it’s no longer possible to usefully transmit sound.
I had an AM Stereo modulator for a while that did 10Khz and on the better radios was quite good. Commercial AM, with a few rare exceptions, isn't a good representation of what one can get at those frequencies. Nor are the radios sold today. They are frankly, terrible!! Get any older AM radio, 80's era and older and it's quite the difference.
Shortwave is modulated at about 3.5Khz, and is enough for speech and the gist of other material.
Noise is the primary reason we do not use those wavelengths. Power requirements go up too, if the signal is to reach max distance. There is a compromise in play, bandwidth vs propagation.
Finally, we also use an emphasis curve where higher order frequencies pack a real punch, with lower ones getting a less due to how sensitive we are to noise at various audio frequencies. Higher pitch noise stands right out, with our peak sensitivity around 3.5Khz.
We can, if desired, transmit a pretty great audio signal at the Khz frequency range. We just don't, because a narrow bandwidth is a better use of the spectrum.
Sound waves are pressure variations in the air. Electromagnetic waves do not require air. They are oscillations of an electric field, which can propagate in empty space. Completely different wave phenomena.
The article has nothing at all to do with sound.
Of course, you can send acoustic information on an electromagnetic wave. That's how radio works. But it's not the sound wave that is transmitted by the radio station - it is the EM wave, with information about the sound wave encoded into it.