"...uh, yeah. For a visit. Have we met?" Larry knows about himself and Cecilia, and he's dimly aware that she knows there are others like them - she's mentioned Arthur and Gaheris, but only in passing. So the vague familiarity is easier to attribute to the fact that everyone buys groceries, right?
Of course, the emotions that go with people he've met that way usually aren't so stomach turning.