Why does Frank not give his address to Miss Kinsman?

Several events account for Frank keeping his identity from Miss Kinsman. Although Mrs. Graham introduces Frank to her at the English Chaplaincy, Miss Kinsman subsequently follows Frank out. When they he sees her, she says she only wants to get Frank's address. Miss Kinsman apparently did not catch his name when introduced by Mrs. Graham. Frank does not let on as to his identity, but offers to walk her to the tram. It turns out he has not yet made up his mind if he should hire a governess.