I will try to answer a few questions here. Social signals are a factor, links are a factor, and user interaction is a signal. I think what has changed is that links without social signals of some kind is now considered unnatural. How can natural links being built come without some type of social signals? Why would people share your site on social networks if your bounce rate is through the roof. I think they are using all 3 to confirm the validity of the others.
Social signals with high bounce rate and no subsequent linking equals false or manipulated social signals.
Links with no social confirmation and/or high bounce rate equals self made or purchased links.