I had a play with this and I think you need to add a vertical section rather than 2 columns in one section. Add it by clicking the + on the left side of the editor (page has to be selected, not a section) and then raising the bottom and lowering the top so you effectively have a section split in 2. Then you can add scroll to one and not the other. Hope this is the correct way 
I haven’t figured out how to stop one section while the scrolling section scrolls though… let me know if you figure this out!!