Psychological stress may be different from physical stress.
As in the article, cortisol did not increase but cognitive decline happened.
This indicates that emotions are more prevalent in stress regarding other activities.
In the sense that these subjects were doing a casual activity, the body was responding to continuous activity noting that emotional stress can decrease performance in ways that are not apparent in this study. Sleep is important for recovery after stress denoting that energy is wasted/expended on activities requiring continuous performance. Under emotional stress, the sustained effort would not happen making it contingent that these subjects are keeping the regulation of limbic systems maintained. In military training often people break down and are then conditioned to disregard all emotional stress to focus on whatever mission or task they face.
