I am not sure if that is true. I have seen Intermittent Explosive Disorder (IED) often in people with developmental disability and I have diagnosed it in children and young adults when I did not have enough evidence for Bipolar Disorder. I see Intermittent Explosive Disorder as a default diagnosis (no other diagnosis can be related to the behavior) and might reflect a person's inability to manage their anger. Another similar diagnosis is IMpulse Control Disorder, which does not always refer to anger.
People with personaly disorders, however, often have emotional dysregulation and if they exhibit this dysregulation with anger, it would not by uncommon to refer to it as IED. People with personality disorder often do not manage confrontation or disagreement with them well.