He didn't say he knows _the_ cure he says he cured himself.
It's like someone loses weight and sticks to it, they don't know _the_ cure for obesity, but they managed to go from being obese to not being obese and staying there for some time and then wrote a blog wherre they say "wow, i found i was over eating due to eating shitty lunches at my desk and not doing exercise so then i switched to salads and cycling to the office, turns out i cured obesity in myself"
It's completely different from putting forward an intervention and then claiming, against all scientific evidence, that this is a reliable and repeatable cure.
A good trick for reading comprehension is to read the last paragraph first:
"I don’t expect this to work for everyone or even most people who are inexplicably unhappy. But I believe that most people can gain some insight by reflecting over how their lives correspond to evolutionary history. " blah blah blah..
This is an incredibly weak claim, it's basically saying "[most] people can gain insight into their emotional state by reflecting on their basic needs and for some people (not all, or even most), that might make them not be unhappy, my evidence is a sample size of yours truly, plus maybe a few people i've talked to who agree".
Wow.
One can often get a different impression of articles by reading only the headline or the first para, which tend to be loaded with attention-getters or rhetorical tricks that are designed to be provocative and hook a reader in. It's easy to make knee-jerk emotional reactions.
Article seems to me, just to be full of rather banal truisms masquerading as science.
But so is just about everything else written on the topic.