Well, they were half right
BBC is running a short feature on the 1947 Roswell UFO thing. One commentator said:
"The aliens look like a futuristic version of us, with big heads and little bodies."
Indeed, the image of the 'greys' goes back at least 100 years in sci-fi. The basic idea was that Future Humans would be totally intellectual, because labor-saving machinery would obviate all exercise. Evolution would then enlarge our heads and shrink our bodies.
Well, the basic concept was right. Modern Americans have abandoned exercise and taken up purely mental activities, with only the thumbs actually moving.
But the futurists didn't understand human metabolism. The result wasn't
like this; it was
like this.