There are a lot of factors that may have correlation to health outcome. The fact that something is correlated does not, as journalists will often suggest, imply that there is a causation effect. The fact that the poor in some locations are more healthy is a good hint that being poor is not the direct cause of their health issues. But being poor is a root cause of many adversities in any society that doesn't treat health, education, and other such things as basic human rights.