Facebook user always habituate with friends connections. Users are always try to make new friend by sending friend request. Though Facebook has limit some of their features that you can't send friend request to more people who are not known by you.
When we enter into Facebook News feed then users small image thumbnail with "Add Friend" option will appear vertically under People You May Know headlines at the right side of the page.
Facebook maybe trying to bring changes in this vertical Friend suggestion bar with large image thumbnail.
Today morning I have just log into my personal Facebook account then I saw the changes. But still Facebook didn't officially announced about this. I have search through the web also didn't get any clue about this change that they have roll out of this feature of not?
I think Facebook is currently evolving this features and old feature will be replaced by new one. There may be the reason for this changes. By large thumbnail it will be more noticeable by users and their engagement will increase and improve.
After changing Facebook news feed their reputation dimmed among the business people because now visibility of Pages reduced significantly. But maybe they are trying to bring some more changes on their news feed to make it more attractive and effective.