Yes the last line is absolutely outrageous!
How she can say such thing so easily? unbelievable!
Well for socialization we normally talk and meet people we know like friends, colleagues, relatives etc etc .
She has him, friends, relatives... i don't think she will get bored from all of these people.
Talking to strangers late night is not socialization. I think its something addiction and this is not good for any relation.
I want to be wrong here for your friend but i think she is not serious with him.
I would suggest that he should try to realize her that its not socialization and its not good. May be that work.
And if that doesn't work he can also try to show that she is also not important to her and do similar things with her like avoid her, talk less, starts talking with other people even stranger... i mean anything which can caught her attention. And if she reacts to it then he can realize her this is what she is doing with him.
But if she doesn't react well then i think she is not serious.