I'm using Ubuntu 17.10 on a Thinkpad T470s (don't think this is relevant) and when I'm scrolling horizontally in Chromium (version 63) and the cursor is in an input box it types j and k characters ( j for left and k for right).

Some additional information:

It works in the address bar and settings window so it can't be any extensions

I'm using wayland on Gnome

The behavior is exactly the same with touchpad and mouse

In the stackoverflow editor box (which I'm typing this very question in) scrolling left does the usual j typing thing but scrolling right inputs a code block which suppose to have the shortcut ctrl+k .

If you want to "experiment" with it and have some edge case ideas let me know and I'll try them.