Healthy people usually maintain the optimal weight for their body structure. (They are not necessarily thin)
Obese people are often unhealthy, as being overweight is also the result of an unhealthy lifestyle and poor nutrition.
Medium overweight regarding their age (who are a large part of the population), are not necessarily healthy but are also not necessarily sicker than others.
Thin people are also not necessarily healthier than overweight people.
Good health is a combined result of lifestyle, environment, nutrition, and genetics.