Even if that's the case, the source that you have cited does not say that ME is caused only by the patients' psychology. From the abstract of your source:

  Personality scores explained 36.3% and 41% of the variance in scores on the anxiety and depression scales, respectively.

This means that 63.7 percent of the variation in anxiety and 59 percent of the variation in depression are not explained by neuroticism or any of the other four of the Big Five personality traits. This is a very far cry from what you are claiming which is that ME is rooted purely in psychology.