Maybe something like: “NOTE: The direction of the arrows is the opposite of the expected direction of the swipe, e.g. left arrow indicates a swipe from left to right”.
I’m afraid “Swing” wouldn’t tell people much, inverting the swipes would be the best option, but if you think that’s impossible, then I think at least adding a hint/warning about the peculiar behavior when the gestures/swipes options are opened for the first time would be better than nothing.
I’ve never seen swiping from up to down being called swiping up, it’s the website that moves up, not the swipe action. If one sees a swipe action associated with the arrow pointing down, like here: https://i.imgur.com/Rvbvh8o.jpeg , then the vast majority are going to attempt swiping down, according to the direction of the arrow. Well, unless they read the entire instructions beforehand, which, as you can probably guess, does not always happen in the real world 🙂