Is there some other meaning in 微笑是一种真实的、热诚的、发自内心的快乐的情绪。? 微笑是一种真实的、热诚的、发自内心的快乐的情绪。


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?
You are correct, "微笑" (smile) is an "expression" (表情) not a "mood"(情绪)

"happy" (愉快/快乐) is a mood. 


一个微笑 (A smile) 
代表 (represents) 
一个愉快的心情 (a happy mood)



  "微笑是一种真实的、热诚的、发自内心的快乐的情绪。" 


should be 

"微笑(代表着)一种真实、热诚、发自内心的快乐情绪。"

(you can omit most of the '的' to make it less wordy)