Even your example of discharging a capacitor can end up with a pulse both directions, caused by the inductance of the wires.
In this specific situation, there's no common reference level, and so the induced pulse will go both directions. You can think of this as being about the edges of the pulse being the parts that actually cause radio to be transmitted, and there's both a positive-going edge and a negative-going edge on a pulse.
In this specific situation, there's no common reference level, and so the induced pulse will go both directions. You can think of this as being about the edges of the pulse being the parts that actually cause radio to be transmitted, and there's both a positive-going edge and a negative-going edge on a pulse.