The key word there is “represent”. Radio isn’t sound. If I make a recording and mail it to you, the delivery time isn’t “the speed of sound through the mail”.

The key word there is “represent”. Radio isn’t sound. If I make a recording and mail it to you, the delivery time isn’t “the speed of sound through the mail”. You can get into a whole thing about trees falling in forests and how a pressure wave only becomes sound when it’s interpreted as information, but that’s totally irrelevant to an experiment about pressure waves through a medium.