While I generally believe this to be true, and I want this study to be evidence that it is true, they fall into the same trap as so many other studies: they can

While I generally believe this to be true, and I want this study to be evidence that it is true, they fall into the same trap as so many other studies: they cannot demonstrate a causal link. It could just simply be that people with worse memories are more likely to enjoy media multi-tasking than people with better memories. In short, correlation != causation.