“body type” has always been a general term to express the entire shape, size and proportions of a person, including excess weight and obesity.
When I was obese I couldn’t pull off crop tops because of my body size, it was incredibly unflattering, and now that I’m a healthy weight I still can’t pull off crop tops because of my body proportions, I have a short torso.
Body type encompasses both scenarios, so it’s often thought of as a polite way to tell someone something is unflattering without singling out specific “flaws” in their body.