Your co-worker seems to have a weird imagination. As pdq points out, it is a simple, straightforward song about lonely country girls longing for the bright lights where the diesel roadtrains are headed. This is how I hear it:
LONELY GIRLS (Ian Tyson/Sylvia Fricker)
Instrumental intro
Light there is golden in the evening Blue shadows forty feet and more When night comes rushing fast 'cross the flatland you'll see Lonely girls linger by the door Lonely girls linger by the door
Linger and listen by the doorway Lookin' down along the fence post line To the highway beyond where the headlights roll on Followed by a low diesel whine Followed by a low diesel whine
Diesels' siren song of the prairies Has a strong pull that never lets go Diesels sing of bright spots with colours running wild Follow me where the evenings overflow Follow me where the evenings overflow
Instrumental break
Light there is golden in the evening Blue shadows forty feet and more When night comes rushing fast 'cross the flatland you'll see Lonely girls linger by the door Lonely girls linger by the door
Linger and listen by the doorway Lookin' down along the fence post line To the highway beyond where the headlights roll on Followed by a low diesel whine Followed by a low diesel whine
Source: transcription from Ian and Sylvia 'Play One More' reissued on disc 3 of The Complete Vanguard Studio Recordings 4CD box set Vanguard 496/99-2.