The Great Gatspy Chapter4, What is the signifignance of Nick's statements: "Anything can happen now that we've slid over this bridge?" and "even Gatspy could happen without particular wonder'"?

Nick sees a limousine pass him with a white chauffeur and black passengers. This is something not seen very often: a white man serving blacks. Gatsby thinks if that is possible than the enigma that is Gatsby must be possible too.