That's not at all an accurate summary of the tweet. You're being a little ridiculous.
If the majority of Arizona students in elementary school are Hispanic, there's nothing inherently racist about suggesting that the border has moved north. It looks like a typical news headline meant to grab attention. I thought it was pretty interesting.
Anti-Hispanic immigration sentiments aren't exclusive to the White supremacist's agenda. Black people often see them as a threat, too. Anyone who is blue collar/working class, can't help but think that they're stealing their jobs. Of course the extent to which they are, is overblown but if you're a white collar worker, it's easy for you to dismiss this as white supremacy or racism because Mexicans aren't coming after your white collar job. Mexican immigrants don't apply for rail lobbyist jobs. They don't apply at non-profits. Those immigrants tend to be dish washers, Orange pickers, factory workers, general laborers - things of that nature. Jobs that I doubt many of you have ever been exposed to or would be caught dead, doing.
Unless you tell me that you mop floors and clean toilets for a living, I'm going to have a hard time taking you seriously when you speak on how ridiculous it is that people are concerned about the mass influx of Mexicans into this country.