Right, I still have difficulty recalling, but I see your point.
I don't know, I used to be quite rounded back in the days of elementary school, and over the summer I stretched out, so to speak. I didn't get much thinner, just much taller.
Maybe it's both, you're metabolism picked up, thus allowing you to take the ectomorph form, it was sort of like activating the ectomorph in you!
Preposterous, I know, but it's late, and that's all I can think of at the moment.