They're not distinguishing it that finely.
The thing with diversity isn't about them actively looking for people around the world (i.e. 'we need to always have a token Filipino-American in the class' anymore than 'we are looking for token Latvian-Americans who will add more diversity compared to Italian-Americans'). The thing is, Americans who are Filipinos may feel they are distinct from Chinese who are distinct from Thais and so forth -- but it's not that different than white Americans of Irish or German or Polish or Greek descent.
Also, I think too many applicants overplay the race issue in admissions -- it doesn't factor in as much as people think. What matters more is your pre-MBA profession, as that's where they do try to more actively manage the diversity in terms of professional backgrounds.