It might also be something like: people who experience relatively little psychological distress are optimistic, and also live longer.

We don't like to talk about it, but there is a biological component to how happy or anxious someone is. Not to say that everyone is doomed to be a certain way because of their genetics, but I've known people who are basically never sad, and it's not because they've found some kind of secret of happiness. I have a friend who has the temperament of a golden retriever.

Or less stressing about things and giving less fucks causes longevity.

Which makes even more sense, since stress affects all cause mortality and all kinds of outcomes, and even mere positive disposition towards a treatment is found to make a big difference in patients.