Unfortunately, that site does scrolljacking, and takes over all scroll actions rather than just vertical ones, completely ruining scrolling on what I think will be basically all laptop touchpads these days (ancient laptops with coarse touchpad scrolling might be less badly affected).

Precise symptoms vary by browser; in Firefox you’re likely to just get jumped from one end to the other very quickly (because it lets the JavaScript take over, and the JavaScript ignores the scrolling delta and jumps by a fixed amount on each event), while in Chromium horizontal scrolling doesn’t get destroyed quite so much, it just becomes flickery, because Chromium lets the JavaScript change the scroll position (turning your 1px scroll into a big jump) and then changes it back, apparently. I haven’t investigated why.

I consistently say that scrolljacking is always bad, because it’s simply not possible to get it right (the web doesn’t expose the right primitives to make it work). This is one of the exceptionally few cases where carefully limited scrolljacking of vertical scrolling to horizontal might be warranted (though it’d still be severely imperfect because the web doesn’t have the right primitives to make it work properly), because of comparatively poor support for this text direction on some devices, but the implementation employed is awful, making it work tolerably for old coarse-scrolling mice while ruining it for newer hardware.