It means precisely that A causes B, B causes A, C causes both A and B, or the correlation is a statistical fluke.
It is intellectually important to be aware of all the options. But "correlation does not imply causation" can be too much of a reflex reaction.
In this particular case, it's easy to imagine how a long commute could cause obesity, divorce, and neck pain; it's very hard to imagine how the causality could run the other way, or what a common cause might be.
The rule could stand to be taken with a grain of common sense.
"it's very hard to imagine how the causality could run the other way, or what a common cause might be."
On the contrary, a (mind that: possible) common cause is even suggested in the article itself: "Perhaps long-distance commuters tend to be poorer or less educated, both conditions that make divorce more common."
In this particular case, it's easy to imagine how a long commute could cause obesity, divorce, and neck pain; it's very hard to imagine how the causality could run the other way, or what a common cause might be.
The rule could stand to be taken with a grain of common sense.