A poor home life in any sense of the term should not matter unless it means the parents are outright abusive. I did not play outside as a kid because my parents emphasized it. I did it because there were kids right outside and playing with them was more fun than anything I could do inside. If one of my parents had to drive me anywhere for me to be physically active, I would very rarely have gone anywhere or done anything at all.
Parents chaperoning their kids every hour of every day _is not normal_ and never has been, except in the US.
> A poor home life in any sense of the term should not matter unless it means the parents are outright abusive
I disagree. Stress from a dysfunctional family or timing demands from being required to act as a caretaker, among other things, will decrease the time and energy required to pursue physical activity.
And physical fitness, high enough to stimulate the indicators they measured, involves more than just causally playing outside - though my interpretation of that sets quite a low bar for the physical exertion involved.
Parents chaperoning their kids every hour of every day _is not normal_ and never has been, except in the US.