This is just my take on the differences or one in the same. Everyone, mentally healthy or not, is going to react to stress. Everyone's feelings get hurt and no one is immune to insecurities here and there. Add these stressors on top of a mood already and of course it's going to feel worse for a while.

I think you are spot on with the triggers and no triggers theory. I've always been under the impression that it's the intensity that the triggers have on you in order to be classified bpd. Like the abandonment issues and what emotions arise when you feel abandoned. Intensity and quantity. Idk I score and feel pretty average with personality so I can't know what it feels like I just know that when a mood strikes generally it's not because of anything but I've been the exception before. Meaning a trauma sent me manic.