Chinese hospitality culture

A few days ago, my friend invited me to his grandma’s birthday party. Since I didn't know his grandma, I refused to participate. I told her that the person I know is you, not your grandma, but your grandma’s birthday party, not yours.
This is a common phenomenon in China. For example, if someone gets married, his brother may invite his friends to his brother's wedding ceremony. But he didn't know his brother's friends at all. Do you understand this phenomenon