Most of the apparel fabric I've seen is a cotton blend, or synthetic.
It could be that the weight of the fabric is different, or the dyes used, or the finish. I recall reading an article some years back that apparel fabrics were typically printed using dyes that would hold up under repeated washings... as opposed to home dec type fabrics that were made using dyes that resisted fading due to light exposure.
My Quilting Treasures sales rep explained to me that there are fiber-reactive dyes, wet-printing dyes, and pigment dyes (in decreasing costliness). But I didn't have the sense to ask what the difference was in terms of longevity of the colors.
In terms of what JoAnn's calls it, well, the can call it "apparel" or they can call it "quilting"... and of course you can use it for whatever you choose.