I would think people's past actions have at least some bearing on my opinion of them.
Based on the few posts I've read on the situation (aka keyhole view filled in from my own experiences), it seems like you're leaning more towards their "side" of the story. Yes, there's at least a possibility that it was a misunderstanding. But maybe not.
Perhaps you, GF, Mr. D and Z should ALL get together and discuss this. That would be my suggestion.