I'm 5ft 6 and was 8 stone most of my adult life until my last baby age 40 put paid to that.
I was slim, yes and size 8. Not much in the way of body fat but I was very fit and healthy. I don't think too thin though. A bit bony at the shoulders and upper chest but if I ever gained a few pounds it went straight to my belly and bum/thighs which I liked even less.
I'm about 9 stone 5 now which is still considered "slim" but I have quite a round wobbly tum and bum (despite still being very fit with good muscle tone).
I think we've got used to people being "well covered" as the norm so anyone who is a healthy lean weight ends up being labelled skinny/bony/emaciated/skeletal.
Most of us eat more than we need, let's face it. I love food!