Why has this version been parented? Shouldn't it be the parent?

That's a good question. While this one is larger, the coloring between it and the other copy gives me the impression that someone decided to alter the contrast and such to "improve" the image. I'd personally be inclined to keep the other image the parent, at least until further evidence is brought about.

I was the one who switched them. This pic has noticeable artifacts especially on the shadowed parts.

"Oooh, I like that, I'll just add it to my favorites and... oh, the parent is already there... from over two years ago."