If the transmission is by wire, then the wire has side lobes which can be picked up. If it is wireless, then its an open electronic transmission which can be picked up be a host of devises including satellites - not necessarily of US manufacture. If the signal is dumped as in the case of Russian troposphere land line transmissions, then an antenna anywhere in the dump circle will pick it up.
the wire has side lobes
WTF is a side lobe ?