More likely he wasn't getting enough veggies and if he was, his system wasn't used to the fiber. Generally, though, there's not enough information there to say what did or did not happen since the only information regarding what he WAS eating was that he cheated on several occasions (in a month's time).
Was he drinking enough water? Taking any supplements? Eating enough veggies? Using a fiber supplement if he was constipated?
Constipation during the first few weeks is not that uncommon. Any time you make a big change in your eating habits, you can have equally big changes in your bowel patterns (either constipation or diarrhea). You'd think, though, that a doctor (psychiatrists are MDs) would be able to recognize that they were constipated and know what to do about it.
The article also doesn't mention what the final diagnosis was. Was he constipated? Just had a bad case of gas? Food poisoning? All are possibilities.