From what the psychiatrist said, I think it's possible to say the self harm isn't in that case unique to Borderline hence it probably doesn't belong on a slide as "unique to BPD" as this could give the wrong impression. I wouldn't want anyone to pin a label of BPD on someone because they self harm, as self harm is present in many mental illness cases.

Also, I believe that self harm as a response to overwhelming emotions is also common in Major Depressive Disorder and Bipolar Disorder from what I've encountered. In fact if you interview a handful of 100 patients with a diagnoses of Bipolar Disorder and a history of self harm and ask why they self harm, I can bet that the majority will mention "overwhelmed" or "overwhelming emotions".

Ive always self harmed when I get overwhelmed by the emotions during an episode otherwise I probably wouldn't see the need for it.

Even if it's the case that the reason for self harm is different in BPD or it is mentioned in DSM for BPD and not Bipolar, I think the evidence points to it not being unique to BPD either way. Despite it not being a unique symptom of Borderline Personality Disorder, I'd say it's unique that it's in the DSM Diagnoses criteria (though it doesn't have to be present, it will signifiy a diagnoses of BPD when present with other criteria).