Board Thread:Speculation House/@comment-68.186.83.101-20130601225528/@comment-4802159-20131028032558

During the sequence where we met Nora, ruby says "You sound just like Dad."

This means that they share a comon person to whom they refer to as 'dad'. It doesn't matter of it's biological. Ruby could have been informally adopted by Yang's family, thereby retaining her surname despite becoming 'family' with Yang.