i'd say you are the one missing the real point....
we also know Mexico is not a Race....
....however the brown kids are implying the white kids are not Mexican because of their white ethnicity....so according to your theory that must also be 'racist'......
It depends on the context.
live in the same world as those kids chanting "USA" and i'll show you "context"......
The kids who chanted it were racist.
If racism is used against them b/c they're white, it's wrong also - but does not justify racism.