My answer, "No, no, that's why I'm not here" should not have been taken since that's very different from "No, no, that's not why I'm here"
Is the person there?
i.e. is the person there (but not because of a circumstance), or is the person not there (due to some circumstance), or can it be either
Since it says "hier" it means that the person is actually there. If she weren't there, it would instead be "da" (or "dort", but that's kinda outdated)
"Nein, nein, deswegen bin ich nicht hier."
"Nein, nein, deswegen bin ich nicht da/gekommen."