The "flat out" thing is a pun, isn't it
Even if that were true, there's technically nothing stopping gravity from being on the x-axis, like in literally any game where you can switch gravity. IT EVEN SHOWS IN REAL LIFE! Walk 90 degrees around the earth, and your gravity will have rotated 90 degrees, sure it's very difficult to replicate since that is 10,000km, but my point still stands.
With that being said, this could just be an x-axis rotated 90 degrees (again, ignoring the 2d images), also, see this: