Says me. Can you postulate a circumstance where art exists in a void? Consider all the things we catagorize as art, and tell me which is not based on the communication of some message. Dance, music, theatre, poetry, visual media, literature: all are communications with other humans or the Divine.
What if his understanding of happiness is different from yours? Should he portray his understanding, or yours?
He should portray his understanding in a way that it is conveyed to others. How are others to understand his happiness unless he relates it somehow to a more universal condition? If I were to paint a series of yellow triangles with great subtlety, crisp and vibrant hues, and hang them in a museum, would you understand the "I'm happy!" message?
Maybe, if you associated the images with happiness, but not because I communicated what they were supposed to mean within the art. Even if I wrote a dissertation on the transcendent symbology of the dialectic between the Golden Rule and the Holy Trinity and the ability of same to distill the essence of joy through pyramid power, it would not change the painting's content, though it might influence your mindset on viewing it.
Art without audience is the proverbial tree falling in the forest. Who cares if it produces sound waves? It may be technically prodigious, but without the participation of another it is ultimately pointless.