Why are they laughing?

All along I knew 妹妹's chinese name is 陈诗璇 and mine is 陈昭绫. I then mentioned "ay, both 妹妹 and my name same same hor? We both got 陈." Mummy and daddy looked at one another and mummy said "of course same lah! It's daddy's surname."

I was feeling a little smart and added "I know papa's name is 陈之财." They were surprised that I knew the artiste name but I changed it later to 陈吃菜. They teased me and gave me a new name: 陈吃鱼(鱼's my favourite),妹妹's name is now 陈喝奶 and mummy is 张吃chocolate.