Good question...

...but I certainly don't get the answer, even coming as it does from an 11-year-old:

But in whatever language, why should Cinco de Mayo matter to Texans?

Because, said Lily, “the country's just right there, and those Texans here in America, we're Mexicans.”

I must admit I am a bit unnerved by this. They may be Mexican expatriates, but still I wonder just how much that kid's being taught she's a Mexican living in America as opposed to being an American of Mexican descent. They should have asked her why it should matter as much as it does to Texans and Americans when it's a comparatively minor holiday in Mexico. There are those who would say kids that age are too young to understand the nuances of the whole thing, but if that's true, the kids shouldn't be asked questions like that anyway.