If we remember anything from college economics courses (and we don't remember much), is that economists love coming up with formulas to explain real-life behavior. And if the formula doesn't fit? Come up with a new one! It's par for the course.
Take the basic concept of production. Production of anything: bagels, TV sets, wonderful Jewy profiles. In theory, if you keep capital and labor the same, your output should stay the same time after time. But it doesn't! With time, you might actually knead more bagels, or make better quality televisions, or write more interesting profiles (you'll be the judge of that one). Why?
The bagel maker might have become more skilled. Maybe the television factory (they still make televisions at factories, right?) improved its technology. Perhaps the writers of Jewy profiles simply have more free time on their hands to do better research! (Who knows, right?) So, why, economists, why?
All those factors create a number that the economists call the "Solow residual", after Nobel laureate Robert Solow. It's a fancier way of saying "we can't really explain it".
That's economists for you.