My current gf is 5’-2” and about 98 lbs. I don’t know what that is for a BMI but she is not anorexic. Not even close. It all depends on the type of frame the person has. My girl has a very tiny skeleton and very little muscle, but a nice amount of soft curves. Her hands and feet are the size of a ten year old child. My pinky finger is literally bigger around than her thumb and that is not an exaggeration. I marvel at how little everything about her is. Even her teeth are tiny. I think my baby teeth were were bigger than her permanent teeth.
As a petite woman myself, I can understand what you mean, but the way you said it is really, really creepy.