On page 18 they power a relay directly from an antenna. This seems a little optimistic to me, or perhaps they had very low-power relays back then?
You would have it installed near your high power transmitter. Having worked on high power AM transmitters, the fences surrounding the antenna can pick up the signal and corroded joints act as a detector, the result is the fence becomes a receiver. So I have no doubt a relay could be powered.
It could actually have been arcing: