The definition of stress may vary upon the perception of the individual but the psychologists have analysed and proposed that stress is the circumstance which can threaten the well being of the individual.
The factors which could be responsible for the well being may differ from individual to individual like the self-esteem may be important for one but not for others, the reputation may be important for some but not for all, therefore, the definition of the stress becomes complex.
The thing wrong with this study is that it could very possibly be wrong, seeing as how it was funded by a candy company. They could have very well influenced the outcome of the study.