I think the author has actually made a very sound point, statistically speaking, that often incremental improvements in dealing with the little things has as much impact on health outcomes as heroic measures to deal with the big risks to health. All around the developed world, mortality from all causes is steadily declining at all ages,
and most of that decline in mortality (and consequent increase in life expectancy) has come about from incremental reductions in risk. Changing engineering standards for highway construction reduces risk of injury and of death from car crashes. Simple checklists can reduce the risk of surgical complications.
A girl with my daughter's birth year in the United States has a better than even chance to live to be 100 years old,
just from an accumulation of incremental improvements in health in the developed countries. The little things matter. We don't have to worry about the little things. Indeed, we can celebrate that so many little things are taken care of for us by societal changes.
To take the author's example of sleeping in the jungle under dead trees, when you first become aware of the hazard, you have to stop and look at your campsite before deciding whether or not to pitch a tent there. Eventually it just becomes part of your background processing when checking a spot, and you would pass up an otherwise nice spot without stopping to think why. If asked, it might take you a moment of looking the spot over before realizing that it's because of the dead tree sitting over it.
If you think about it, it's a lot like developing good practices in coding. What at first is something you have to think about quickly becomes second nature. For example: why do you (possibly hypothetically) use curly braces around a single line block following an if statement in a C-like language?
Several reasons if you think about it. First, so that you can't forget to add them in when you need to add another line. Second, because it makes it unambiguous which if or else if an else belongs to if you have a big nasty chain. You don't spend a lot of time thinking and stressing about those reasons every day, but having the habit protects you anyway.
Well, it's his choice of words. You seem to be trying to redefine the article to your liking.
You're right, rules like the curly braces one you mentioned eventually become second nature, such that you don't think about them. That's a "habit of thinking", as you say. That's clearly not what the author is talking about. The author uses words like: "hypervigilant", "obsess about the wrong things", "verging on paranoia", "constructive paranoia", "I remain alert", "I try to think constantly", "being attentive to hazards".
He's talking about an attitude which might very well bring about stress. It beign second nature to add a curly brace after an if statement doesn't.