A quilt is, by definition:
1: a bed coverlet of two layers of cloth filled with padding (as down or batting) held in place by ties or stitched designs
or...
2 something that is quilted or resembles a quilt
Sooooo...a wall hanging is a quilt. It's just a small one.
Also, I have seen some very intricate mini's that I'm sure take as much or more time than a full size quilt.