The text you quote says is that if you turn your radio transmitter on, and broadcast on a lot of different frequencies, and turn your radio off - all the differ

The text you quote says is that if you turn your radio transmitter on, and broadcast on a lot of different frequencies, and turn your radio off - all the different frequencies arrive simultaneously too(since you transmitted them simultaneously). It will of course arrive some time after you transmit it, since the signal travels at the speed of light. tldr; It's just saying that a low frequency signal travels just as fast as a high frequency signal.