Okay, I understand what rubbed you the wrong way.
It means two things: I'm not, uh, assertive enough to continue arguing about things I'm not an expert in, and gave up at that point. And: I do suppose that Kathleen would be more familiar with the semantic nuances of English words than either of us.
After looking it up, though, I think you're right (both of you, I mean). My initial impression was that you were arguing from an "assertiveness course" kinda point of view, which would naturally try to teach "good" assertiveness (i.e. not blowing up, not being pointlessly aggressive). I, however, thought Kahvi was indeed assertive, and that "acting wisely" had little to do with it. Meaning: she may blow her top every now and then, but that doesn't mean she's not assertive. Just that she's not always assertive in a "wise" way.
And I'm sorry, I didn't want to make you feel not taken seriously.