I would think the difference is that sociable people feel comfortable even in a less formal gathering, when you don’t know of anyone you would particularly like to talk to and nobody has asked you to talk. Even in such a situation, a sociable person could find something interesting to do, involving other people, and be reasonably confident that they are not being rude or boring, and end up enjoying whatever they find to do.
I would think the difference is that sociable people feel comfortable even in a less formal gathering, when you don’t know of anyone you would particularly like to talk to and nobody has asked you to talk. Even in such a situation, a sociable person could find something interesting to do, involving other people, and be reasonably confident that they are not being rude or boring, and end up enjoying whatever they find to do.