Very possible- I don't have the study on hand, so I can't check how careful they were with their statistical analysis. (Ideally, you would have enough information to separate out the successful people who sponsored and the successful people who didn't, then compare them, but assuming a study is ideal is rarely a good idea.)

I do consider it likely that having someone depend on you makes people more likely to stay sober, but causality the other direction is also strongly likely.