I am adopted and my adoptive parents are my parents, duh.
So blood does not matter much to me, but the ties.
Speaking of family, I live with my parents and my sibilings because they are family, but if I could choose, would not want to live with futile people like them.
I get along well with some cousins, and others I have a cordial relationship but do not have much to talk about.
I think family is not all, theres others ties that are so important.
About the unknown cousin, I would not care much. But he was a nice person, I would try to connect with. Like in any situation where i know an interesting person, regardless of family ties.