I've said it before, and I'll say it again... "Seek and ye shall find"! If you are actively looking for any social attitude you will eventually find it. Racism seems to be at the top of some folks' "scavenger list", and being both hypervigilant and hypersensitive will do nothing to eliminate feelings of racial superiority/inferiority. What the hypers will do, is cause people who are inclined toward racism to simply harbor those feelings, and only openly share them with those they know to be of like mind. That closet racism will last only until they work themselves (and probably several their like-minded friends) into a frenzy as the emotional pressure builds and they begin acting out. That's when the SWHTF. Sound familiar? That's how the KKK and the ANP began.
Now to the original post in particular. One of the responding posts to the OPs news link claimed that he had witnessed the event, and that Mexican kids from the mostly Hispanic school had begun the racially charged chanting, and that the USA chant was begun by Mexican kids from the mostly white school. He also claimed to have addressed that issue to school officials, and was told by those officials that, "We just want to get it behind us." I wasn't there so I have no idea what the real story is... and probably nobody else in here was there either. Who knows for certain how it was intended? Only the kids who chanted "USA". Personally, I think it's little more than left-wing, hypersensitive, race-baiting BS. But that's just my opinion. Pax...