It is bad analysis by the reporter but it's also a bad map. Once the tweet-density becomes higher than the maximum point density the area turns red. So any den

It is bad analysis by the reporter but it's also a bad map. Once the tweet-density becomes higher than the maximum point density the area turns red. So any dense concentration of people is shown as red. Find a crowded poor neighborhood and it'll be red. And it's compounded by the way red pops out more than the green does. Also compounded by the annoying zoom level restriction.