I quite believe those anecdotes... a lot of electronics will "detect" a radar at appreciable distances.
All that's needed is a lack of shielding and something non-linear, like a diode, a transistor, a mixer tube in a radio receiver....
When I had a car without a cassette player, I took my home cassette player along, lying on the seat. It would "beep", matching scan rate and prf, whenever I drove past the local airbase, with the radar at least half a mile away.
And I remember playing with a tiny dish (10" or so) from a surplus Hunter gun-ranging radar. Just a diode in the waveguide, and a few stages of audio, and it would pick up aircraft weather radars 20 or so mile away.
CJ