what makes a painting a painting?

I was working on this little piece today and I couldn't help but notice the sheer volume of paint on the backdrop surface. This is where I discharge excess paint from my brushes, or mix colours as I go.

Since a picture is worth a thousand words, the second shot below, pans out to show the small painting imbedded in the backdrop.

Looking at it, one might well ask just exactly how much paint is not on the painting itself. And then one might further ask, is the 'intentional' painting (the one I set out to paint) really any better than the unintentional painting. The intentional painting benefits from conscious effort, a trained eye, and a certain amount of discipline. But the other one, the one I didn't mean to paint, perhaps benefits from not having those very same qualities.

Over the years, I've had many offers from patrons wishing to buy my background wall(s).
Are they on to something?