Triangulation, positive and negative, is a big part of the BPD playbook. They often set up a third person or party as the perpetrator or benefactor and then proceed to dump their unfiltered emotions about them to you.
My ex talked
PLEASE READ about my best friend and then proceeded to date him immediately when I gave into her demand to have a break. Also the random guys on social media who shared her interests went from the coolest dudes ever to the creepiest of creeps when she let them too close (and thus also cheated on me emotionally).
Ultimately the triangle often spins around and means very little. It can be an awkward attempt at obfuscating the truth ("Don't worry, I could *never* imagine dating him, he's a creep!") or just an example of their weather vane spinning about. It's got a lot to do with their black and white world. The same object may appear the best or the worst on a whim.