As the man (whose name was Edward, by the way) walked around Chinatown, he took notice that besides himself and that cute couple he met earlier, everyone down here was straight. So that prompted him to absentmindedly say out loud "I wish most of the people in Chinatown were gay guys. Then it'd be way easier to find someone." Looking for a boyfriend down here was like looking for a needle in a haystack. Well, soon, it would be more like looking for a needle in a needlestack.
After making his wish. reality changed, rearranged, and reconfigured, making Chinatown the new desired destination for gay men. The bar that Darren and Ben had been in (which was on the outskirts of Chinatown) transformed into a popular gay bar (with all of the people already inside it becoming gay men), and a multitude of residents who lived in Chinatown became gay as well. If they were female, then they became male, and gay. If they were already male, then they just became gay. And since reality was re-written with Edward's wish, no one (not Edward, or Darren or Ben) remembered the previous reality. Everyone who was changed thought that they were supposed to be male and gay.
But there was one person who did notice that things were different. And that was the old Chinese man who owned the ointment store. Being associated with magic himself (in some way), he wasn't affected by the wish, which validated Edward's wish, since he wished for most people in Chinatown to be male and gay. Everyone but the old man qualified as "most people". But what would the old man do about it? After all, he knew what the ointment did, but sold it to Darren anyway. Obviously, he must have known something like this might happen. Right?