As someone who "eats healthy" and maintains a healthy body weight (through a combo of eating the right amounts + exercise), I couldn't disagree more. I eat less of my salmon, yes, but I'm still paying $4 per meal when I eat wild caught salmon versus $0.50 for that pre-cooked-chicken-from-a-bag.
The article states that the unhealthy food costs less per calorie amount. So assuming that the average person naturally eats ~2000 calories a day, whether healthy or unhealthy, the healthy food costs more.