I think you are right about the insurance issue. Better to leave the diagnosis somewhat vague for them so they don't get restrictive.

I can see that description your doctor used as being another way to say Borderline PD and many insurances do not provide coverage for personality disorders, so it would make sense to use a diagnosis like unspecified episodic mood disorder.

I can also see how the diagnosis feels vague to you, so I hope you'll talk to your doctor about it, so you can feel better.