I'd like to watch this documentary. Do you know the year and/or channel where you saw it? The antenna is focused with a tremendous amount of gain towards a spot in the sky, and provides a very significant amount of rejection to signals in all other directions. I can't see how you would get a signal at 1.42 GHz from a watch or flashlight. Harmonics from something like a walkie talkie only occur when the radio is transmitting, and they would spread in bandwidth at each successive harmonic. It would have to be an extremely narrow fundamental frequency, with no audio signal on it, to get a signal with less than 10 kHz at 1.42 GHz.

https://m.imdb.com/title/tt7928816/

I don't remember where I watched it, but the 2nd and 3rd links from a kagi search were for Prime and Apple TV.