I think Mexican "skinny" and American "skinny" used to be pretty different. Being thin and curvy was bomb in mexico before the culture started to disseminate with lots of facebook and name brands etc.
I remember when women used to aspire to being thin but not skinny. Now it's cool to be super thin and flat to look like Abercrombie models. So maybe Mexican women when the writer asked the question seemed less uptight than American women at the time.