This new study that did not find a causal link was part of the attempt to find out how. The original study was more of an observation than a deep dive.

You could think of it similar to a study that shows something like "People who don't watch network TV have fewer strokes", which could be an interesting correlation, but the causal effect might be something more like "people who are more health conscious tend to avoid sitting down for extended waking periods" which ultimately has nothing to do with TV.