The author is unable to differentiate happiness and pleasure !
No, the author is very well able to differentiate happiness and pleasure. The brain is clearly wired for pleasure, it has an extensive reward system that can even be tricked into working overtime (leading to addiction).
His point is that our brains have a natural bias towards storing and recalling negative experiences over positive experiences. We have evolved to immediately learn from physical and emotional pain because learning to avoid pain is a better survival strategy than learning to seek pleasure.