Why was Theroux fascinated by the taxi driver's offer of a prostitute in the Bay of Bengal?

Theroux had been offered prostitutes at other places during his voyage, but the taxi driver in Madras was specifically offering him an "English girl." Although it turned out to be false, it intrigued Theroux, who tried to imagine how an English girl could have ended up as a prostitute in a poor Indian community. He had wanted to see how she had ended up in this situation.