I would be bothered by the comment, simply because he's a pdoc. He prescribes meds. That literally does not work without a label. Different problems need different meds.

So if you bring it up, maybe frame it a bit like that? Tell him your meds don't work, and you'd just like a second opinion to be sure? It is of course possible that their diagnosis is correct. Meds often do not work for BPD. But even then, better rule out everything else before assuming it's not that.