[andrewflnr]

I mean, I've noticed most science journalism is bad, but this one made me feel like I was having a stroke.

And the perspective of positions on the core and surface moving relative to each other in some cylindrical coordinates may well be what the article meant, but they sure didn't make it clear, and it's ultimately ill-defined: the correct unit for that change is still an angle. A particular linear distance can only accurately describe it given a particular latitude, which is expressed in, guess what, an angle. This is of course an overly technical way if explaining how the "moving" terminology just obfuscates a pretty simple and accessible underlying concept. They went out of their way to make it less clear.