Well, "health" isn't unidimensional, but one of the key areas (and one, but not the only, key risk area from obesity) is cardiovascular/respiratory health. Being able to run a mile (or not) is a much more direct indicator of that than obesity/non-obesity is, so at leas in that area of health, it makes sense to see an obese person who can run a mile as "healthier" than a ideal-body-fat person who cannot.