I think my daughter read about BPD when she was trying to identify some of her own suffering symptoms and then was confirmed later after testing. I think it might be important if your son is self identifying as BPD to believe him or rather give him the benefit of the doubt.
DBT therapy is helpful and if you can get some guidance maybe byway of reading about the condition it MIGHT be helpful as a tool to relate to your son. I think we all want to be understood and it can feel relieving for someone suffering to put a name to their condition. At least it was for my daughter. I take the approach that this is an illness and it is. A very complex rollercoaster illness that my child is suffering from too.
The DBT education can help give tools as to kinda standardized thing that might be helpful to diffuse things etc. more times than not the tools work with my daughter, but it can be an exhausting experience when in the thick of it all.
I hope we are all here to support each other and my only kind of thinking is that if your son thinks it could be BPD or he’s pushing that as his diagnosis? Believe him and just try to educate yourself and stay stable. I hope this helps. I really do.