What intrigues me the most is not that people said they knew of it, but that they had a formed opinion for or against. If they didn't ask about Simpson-Bowles to the same people, then maybe as you suggest people had an opinion on S-B but misremembered and thought that this was the topic. But if they did, then the only explanation I can think of is that 8% of the people have such a strong positive prior for "bipartisan plans devised by a Clinton Chief of Staff/former western Republican Senator combo” that they agree with them without knowing what they are, and the reverse is true for 17% of the people.