Is it wrong to not care about my friend's family?

My friend talks about her family and family problems a lot more than any friend I've ever had and its at a point where I'm just questioning why she thinks I care that much. Recently she gave me her brothers phone number to tell him happy birthday... I've never even met him. And I don't know if this is a bit much but it just feels like a weird thing to do especially when I don't trouble her with my family issues. Like its not my fault her brother has no friends so why does she expect me to treat a practical stranger as a friend?

Is it wrong to not care about my friend's family?
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