I'm inclined to go with the 2nd harmonic theory.
The non-approved just-above medium wave naughty cordless phones had a very noticeable output in the 80m band. Being illegal, there was no oversight of spurious emissions.
One local entertainment for radio amateurs was a woman in the Dunfermline area who regularly made assignations to meet her 'fancy man' at the phone box at the bottom of Garvock Hill. There was enough info for those with local knowledge to identify them, though those knowing, had the good grace to not reveal the names. It went on for quite some time. I suppose spilling the beans would have ended the entertainment, and we could always take cover behind the clause of not revealing the content of anything intercepted not specifically allowed by our licences
The nature of what was said made it quite clear that there wasn't the faintest inkling that what was being spoken into was a radio transmitter. I guess the same is still true.
David