The first I heard anyone from a search engine talk about using click-backs to the SERP it was Duane Forrester form Bing, not someone from Google. Every search engineer I've talked with at conferences has described click-backs as a noisy signal.
So there needs to be a lot more involved in extracting a strong signal from a click-back pattern - time on page before the click back takes place would be a possible factor. Other possible signals might be "did the user scroll the page before clicking back?" and other potential engagements signals.