Why such a casual groove and feel for such a sad story?

I was listening to a song by David Tao, it's called "Susan said".
I never looked at the lyrics and thus never knew it was about, cuz you have to know, Tao is not so clear in pronunciation.
Anyway, I took a look at the lyrics just now, I was shocked by the crazy story happened in the words. I can't believe how could he put such a casual and happy groove and feel in to this bitter story of a poor woman.

The lyrics:

"Yeah 蘇三說 Susan 在那命運月台前面 再上車 春天開始落葉 轉接間 話斷了線 離台北 南京是多麼遠 Oh 那諾言 還會不會兌現 Yeah 不在乎愛情裡傷痛在所難免 一個人卻一個世界 Oh 你是否也像我 動搖過幾遍 愛之是個錯覺 Oh Yeah 蘇三說 思念 常常想念不常見面 她懷疑Sam是虛擬的臉 但愛情 還在上演 那是誰 在放古老唱片 那片段 像對未來留言 不在乎愛情裡傷痛在所難免 一個人卻一個世界 Oh 你是否也像我 動搖過幾遍 愛會不會實現 Oh "蘇三離開了洪桐縣 將身來在大街前 未曾開口心慘澹 過往的君子聽我言" 蘇三離了洪桐縣 掛了個牌子在那大街前 被那凶惡群眾包圍 稍微 等一下 過往的君子請你聽我言 哪一位去我南京轉 與我那三郎把信轉 就說蘇三把命斷 來生變一隻狗一隻馬 我當報還 不在乎愛情裡傷痛在所難免 一個人卻一個世界 Oh 我懷疑你像我 動搖過幾遍 是否愛本來善變 Oh..."

Looks like the story is about Susan from Nanjing who was living in Taipei, because she thought she moved in with a man who loves her, Sam. And apparently Sam wasn't as good as he looks, maybe she's his mistress (very common story). He didn't really give a shit to her after she got to Taipei, his face was almost like a computer generated image in her memories. She decided to end her life, and asked somebody to tell her husband/lover back in Nanjing that she will payback what she owed to him in the next life, to do so, she is willing to turn into a horse or a dog, she doesn't mind.

Sad story, but Tao used some really bouncy groove and major key and happy mood.

Isn't that ironic? For a great musician like Tao, I'm sure he did that purposely. It such a big contrast that when you find out what's in the lyrics, you would start to tear!

David Tao, man, he's something...