I'm guessing the numbers in combination with some other keys allow you to assign that particular keyword.
When I click and hold, the panel scrolls but it's weird that you have to exactly click the numbers to scroll the panel.
Thanks for opening my eyes! After some more experimentation, I found that the hand is only there to scroll the side panels. And one does not need to click exactly on the numbers - I was wrong. It works the same on either the left or the right panel - I was in Solo mode and therefore no scrolling was possible.
As for the numbers, I think they are displayed to show the nine more recent keywords or the nine keywords in the selected keyword set. I haven't found a way to use them.