'Fat but fit' may be a myth, researchers say

The WP author here confuses correlation with causation.

Both obesity and fitness response to cardio (e.g. measured by VO2Max) have genetic factors (many obese people are genetically low-responders to cardio). See the recent University of Bath study for details.

It was a never a truth to begin with, really. Even the original study was rather controversial in its results. Fat but 'fit' is a transitory state between healthy weight and fit or obesity and unfit; eventually all that weight will catch up with you.