Yes, possibly Job. But the Ranchero came out for 1957. And the El Camino didn't start till 1959. So Ford clearly had a head start.
Also of possible interest is the 57-59 Ranchero was based on the full sized car. And the 59 and 60 El Camino was similarily based on the full sized car.
But in 1960, Ford changed the Ranchero to the much smaller compact Falcon size. While the El Camino was still big in 1960. Maybe Ford's change to compact size in 1960 "confused" Chevy so much they just dropped the El Camino for 1961. Then when Chevy brought back the El Camino in 64, maybe they just took the middle ground, and based it on the Chevelle size, as previously noted.
My thought remains the same; who knows what any of those Detroit auto geniuses were thinking?????
Keep in mind - there were no compact Fords or Chevys prior to 1960. You had full size, T-bird/Vette, and trucks - that's it.