It looks like they adjusted for the common cofactors. There could be more they missed, but this study is also backed by a large body of research that found similar effects. You can see some of these other papers in the references.

Probably the effect is driven by several factors including mental well-being, increased social cohesion, reduced air pollution, increased opportunity for exercise, and other things. Frankly, it would be surprising if these things did not have an effect on lifespan.