Earlier quoted context omitted.
What I'm getting from this is that you don't know your "friends" particularly well. How do you know how well I know my friends?
I think you underestimate how common it is for people to use names other than on their birth certificates, passports or marriage certificates.
On the contrary, I am friends with such a person. We've talked about it.
Actually, I am friends with many such people, if you count Chinese people using English names. There is a mode where I don't know any part of a Chinese person's name, but there's no mode where I know their personal name but not their surname.