need some clarification about the encounters with the african guy

I don't think that there is any sort of clear answer as to the meaning of Albert running into Stephen (the Sudanese guy), or if there is any meaning at all. Caterine links Stephen and Albert at a very simple level, that both are orphans in a very broad sense. I don't see this as contradicting her philosophy, since she sees suffering, cruelty, and loneliness as universals common to all people. When you take on that viewpoint, every instance of pain or betrayal is connected together as a confirmation of your view.

Although the Jaffes see everything as connected together, it does not necessarily follow that there is a reason for every coincidence. Maybe it would be better so say that there is not necessarily a simple reason for every coincidence. For them, trying to explain the connection of things requires a great deal of evidence, as shown by their constant evidence gathering, and in the scene after the one with Albert's parents. In that scene Albert asks them why they didn't make the connection that Caterine did, and Vivian responds, "Because you lied to us. You told us that the African guy was the doorman at your friend's building, not at your parents' building. You encrypted the truth." If everything is connected together as parts of one big blanket, then it's hard to explain what's going on in any one part of the blanket without having a good understanding of lots of other related parts of the blanket.

-- TopFrog