Whoever said this only demonstrates their immature and superficial attempt to play with words. In simple terms, this expression means "only grateful individuals are happy". Because something sounds good doesn't necessarily make it true.
Babies and children are generally happy, does that mean they are grateful too? What do they even know about being thankful or grateful? I don't think anyone can deny the fact that children are human beings like anyone else, and that, generally speaking, they are not thankful yet they are genuinely happy.
Being thankful is one way of expressing gratitude. Gratitude itself is a sign of wisdom which is a result of lessons from living fully the experiences that life unfolds before you. Real wisdom and humility go hand and hand because a wise person is someone who understands the greatest lesson from their own wisdom: “What they know is insignificant compared to what is there to learn”. That is why wise individuals are generally quietly humble and they are thankful for any additional drop of pure knowledge that life brings to them as a gift.
A wise person experiences life fully with an absolute conviction in the simple fact that everything that happens to them is done with Love and Justice. This alone removes any possibility of experiencing low-level feeling such as envy, hatred, anger, and so on. A person who reaches this level of wisdom is nothing but an embodied living gratitude themselves.
Someone who is genuinely grateful lives to give not to take because they truly become a mediator of what life offers in abundance. They know that they are too small to contain everything that life has to offer therefore giving becomes the only way to further growth, expansion, and eternal renewal that guarantees freshness or life itself. This type of individual gives in silence. Just their presence alone is powerful enough to influence their surroundings. This is why many people feel something uniquely great and powerful when they find themselves in the same room with a person full of wisdom.
Those capable of following and understanding these explanations will easily understand that, in all truthfulness, Happiness is not a static state but a consequence of a constant movement between giving and getting that unfolds at a higher frequency that seems like it is static. It is like the blades of a helicopter that rotates so fast that sometimes they give the impression of being static or even rotating slowly backward.
The natural exchange between giving and getting is what I constantly refer to as “The Natural Flow of Happiness”.