You were working at the Armed Detective agency,while no one was around you decided to play a instrument to relax for a little bit,you were good at it too.You thought no one was there,when you stopped playing the instrument.You notice her at the door,she claps her hands.You were a little suprised that she was there,see you playing a instrument.

“That was good! I didn’t knew that you were that good in playing instrument.”

Yosano didn't say it just to show off, she seemed genuinely impressed.