"This research only suggests a causal association..."

This wipes out the assumptions that most people seem to be making.

People who are active sit down less. People who are active have a longer life expectancy. So be active. QED.

Nothing about this says that if you change your behaviour by sitting down less, you will live longer. Even TFA acknowledges this.

Conclusion: this article tells us nothing new, and nothing that we wouldn't have assumed already.