I define a quilt as a type of blanket with two layers of fabric stitched together with some kind of batting in between. (Of course a whole cloth quilt is a quilt!) I give credit to "quilts" that are not quilted, but tied, and to those that don't have batting (such as Cathedral Windows quilts, summer quilts, yo-yo quilts, etc.) A bag or garment that is quilted is not a quilt, but it is a quilted item.
I actually think that definitions are important for clear communication, but I wouldn't argue with another quilter about whether her item is a quilt or not. What purpose would that serve?