Love that!

I understand from seasoned quilters that using printed fabrics for backings will hide any minor mistakes you might make while quilting. Solid color, muslin, etc tends to show every stitch.
If you're short of fabric to complete the backing, many quilters work in extra fabric from the quilt top fabrics. You're the only one that knows this didn't start out as an artistic endeavor.
I currently have waaaaaaay to much calico print in my stash, so I'm currently doing a simple patchwork of these and using it as backing. When I get tired of that, I start using something else LOL
I guess the bottom line is whatever works for you "it's a good thing"

I love pieced funky backs.

I like my back to compilment the front as much as possible
this where you can find backsides if you like
backside fabric.com

I don't like to peice the back so I love it now that you can buy the extra wide fabric!

This is new to me, too. I've only seen it here, but I think it looks so cool I've started doing some of mine like that, too.

Oh, that's as cute as can be!

I love some of the leftover fabric incorporated onto the backing. Gives a plain back some character! I know some quilt judges have admired the creativity of backs and didn't give or take away points on thie judging the quilts.

Usually it is because there isn't enough backing fabric for the width of the quilt. I personally look for a fabric with a pattern of some kind that I can use as a quilting design. If I don't know what to quilt, I can use the design of the fabric, and put the quilt on the machine upside down( backing on top). Works for me!

Nicely pieced! Looks like you intended it to be that way.