First, I want to say that though your move only fixed it coincidentally, I see what you were going for and it was a good idea. See something is broken, undo a recent change to see if that fixes it. And it did! But in this case the only thing changed was image description text, which shouldn't really make any difference.
So why did it work? It's a weird Wikia error that screws up images on pages, and anything that forces the page to get recreated (like an edit) causes it to rebuild it and give it another chance at getting it right. FriggyEsquire was recently asking about it on the forums, so you can read a bit more about it there, and a simpler way to knock things back to working if you notice more screwed up pages.