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.