There's a pause while Riddick weighs his options. He's moderately sure that this whole name thing doesn't actually bind him to her any more than they already are-- and he's actually okay with breaking any implied promises to somebody like her. And while it could be seen as an implied promise, he's not actually sure how she'd take it.

Hmm.

So after that pause, he answers, "Well, she ain't here, is she?"