Total speculation here TMC, but could the part that was "bombing" him have expected that somehow, because this happened when you were going to therapy, he should have protected you from it? I know that's not rational, but then feelings often aren't. Was (s)he punishing him for letting you get hurt in "his" car park, on the way to see him?

Or, in a similar vein, did he perhaps say anything in the first moments of therapy that didn't feel sufficiently protective of you or concerned about you? Such that a protective part might feel like he was failing as your ally?