I like the way you express this. “Cis / Trans” isn’t about your gender, it’s about whether your gender has CHANGED. (Although it may not be your GENDER that changed, but what people THOUGHT your gender was.)
In a similar way, I (a cis male) usually call myself “straight”, but that’s not really accurate. I don’t feel like I’m attracted to whatever gender is different from mine (which happens to be women); I feel like I am attracted to women (which happens to be the gender that’s different from mine).
Putting it differently, if some magical spell were to transform me into a woman, I don’t imagine that I would then be attracted to men, I imagine that I would be attracted to women. So instead of calling myself “straight”, I should probably be saying that I am “gynosexual” (attracted to women).