From my understanding, DID is not a well accepted diagnosis my psychologists. I can't comment about this person specifically, but in many cases people diagnosed with DID actually have borderline personality disorder. It's a condition characterized by an inability to regulate emotions. They tend to experience their emotions in the extreme, regard others as either entirely good or entirely bad, etc. People with this condition are also very emotionally fragile, and are very suggestible. If a doctor starts asks them a leading question about having multiple personalities, they may internalize that and act accordingly.

Source: my father, a clinical psychologist