I actually heard that particular numbers station a couple of times when I was a girl in the 1960's, playing with my parents powerful shortwave. I called my mom over to listen, and after puzzling over it, decided it must be some little European kid fooling with the parents' ham radio. "She is going to really get in trouble" I remember saying. Another time I heard what I now know was the East German Stasi dissonant "gong" transmission, and thought it was just astonishingly bad music, and felt sorry for people in whatever culture or country it came from. The Morse Code transmissions, common then too, I assumed were some kind of secret government communications.