I didn't suggest that people ate low carb back then, though in my experience (born in 1951) we ate fewer carbs than the average younger person does now.Well, my history seemed to be the same as yours.
I certainly didn't see any "low carb".
We didn't snack as much, and we exercised more running around outside.
I was thin then, I got fat later when I had more disposable income to spend, and sat around eating the snacks I spent it on.
I'm not blaming the world for it, I did it to myself. No one made me eat all that food.
In fact, the only thing I remember about that, and the NHS, was every time I saw my doctor, she told me I was putting on weight, and to eat less, and lose some.
Certainly not forced onto a diet that made me gain more!
What I did say was that (in general) we were 'fat adapted'. This means being able to switch without difficulty from using carbs for energy to using our personal energy store that is our body fat. Thus we were slim and didn't need (nor have) snacks versus the currently overweight population who at least feel they need to eat 6 or more times per day (encouraged by the food manufacturers).
In my particular experience in the late 1980's my GP started telling me I must eat low fat high Crab in order to ward off the heart disease that killed my dad at age 45. I was still then (BMI around 22). I had my doubts about this because 1. My dad was a chain smoker for most of his life and 2. When he gave up smoking he became overweight 3. Physically I take after my mum rather than my dad.
However under the pressure of doctors, NHS, government, media, friends etc. I slowly caved in and ultimately went onto a very low fat way of eating indeed with large amounts of wholegrains, fruit and carrots (on which I was told to snack).
Inevitably this made my weight increase because 1. Due to all the fruit and grains I was consuming more calories 2. My calories were mostly in the form of carbs.
Because of my (low) weight and low blood pressure, I was never advised to lose weight until my Type 2 diabetes diagnosis two and a half years ago at which time (by using the BMI range) I was a whopping 2 pounds overweight!