The GP comment is about a three year old. Not old enough to be playing a block away with friends.
It was when I was a kid.
I trusted my then-3 year old to be 250' away at the opposite end of a neighborhood park that abuts my house. Usually within eye sight but not always.
Once he reached 5 and showed they understood the boundaries and requirements, to go out there by himself.
And once he reached 6, he was trusted to look after his 4 year old brother in this space.
And these restrictions seem very strict compared to how I grew up and especially compared to how those older than me grew up. Or in some other places in the world, where e.g. in Japan it's not rare for 6 year olds to ride the subway and do errands and downright common for 7-8 year olds.
Absolutely, 100%, no.
A child could be playing out of sight of a parent, maybe a block away with friends, and get mildly injured in a way that requires minor treatment. Or just crying because of a negative interaction with a peer.
This DOES NOT mean children at a certain age and maturity level cannot be trusted to gain some independence and leave their parents line of sight for short but increasingly longer periods of time.