Take away the descriptive elements and it says:
微笑是情绪。 （A) smile is (a) mood.
Maybe if they said: ‘一个微笑表示着一种真实的、热诚的、发自内心的快乐的情绪。’ Would that be acceptable??
A smile is an expression of a mood, but not a mood in itself. I have to think of these lines from a song: 'I smile when I'm angry, I cheat and I lie, I do what I have to do to get by.'
Am I missing some meaning here?