Those things were known before psychology named, published, and formalized them. They were just called "common sense" and presented alongside a number of competing ideas. Buddhism is no different in this regard: everything it gets right is not known to be right until someone uses a reliable process to verify it. Until then, there is little reason to accept it as a known truth.
Cognitive Behavioral Therapy (CBT), for example, as one of the few proven effective approaches in therapy, is in many ways not so different from (zen) Buddhist practices. And the growing body of research on meditation and mindfulness is at least indicating that these things are very good for an individual's well-being.
While I personally do not care much for the more spiritual and religious sides of all this, I've definitely become less dismissive of these things.