Gossip Girl: The Princess Dowry (S05E17) contains the following exchange:
William vdW: I'm just sorry that Eric couldn't make it back from Zaire.
Serena vdW: I think they call that the Democratic Republic of Congo now.
William vdW: They do, but trust me, it's not.
William van der Woodsen refers to the Democratic Republic of the Congo as Zaire and is corrected, but replies "They do, but trust me, it's not.". Can someone explain to me what this comment means.