Well he wasn't going to change over night. On top of that, he wasn't going to suddenly start caring about things he never cared about before. It was a big enough step for him to begin to say 'maybe I can do this' as opposed to immediately thinking 'No I can't'.
"Girly?" Tsuna asked, tilting his head to the side. How was it girly? "It's sophisticated, isn't it?" That's what he always thought. The guy playing the piano always had a tux on and stuff. "You know the guy on the piano is the most important part," he pointed out. "The other people don't sound good without him." Even the star violinist needed the piano accompaniment or they just sounded hollow.
Tsuna smiled. "It figures a smart guy like you would know how to do classy things." He just kept it a secret cause he thought it wasn't cool, right?