It wasn't the observation of a smart aleck but that of a truth-lover or a statistics-lover. I replied that some of us never drank anything but tea. (11-12)
The "otherness" of the American soldiers is highlighted here – they're out of place in this small English town, and their perceived difference is notable.
I bit into a piece of toast myself, and commented that there's some mighty rough country around Ohio. "I know. An American I met told me. You're the eleventh American I've met." (21-22)
Americans are something of a novelty to Esmé – she collects them like any other interesting and strange item.
"You seem quite intelligent for an American," my guest mused.
I told her that was a pretty snobbish thing to say, if you thought about it at all, and that I hoped it was unworthy of her.
She blushed – automatically conferring on me the social poise I'd been missing. "Well. Most of the Americans I've seen act like animals. They're forever punching another about, and insulting everyone, and – You know what one of them did?"
I shook my head.
"One of them threw an empty whiskey bottle through my aunt's window. Fortunately, the window was open. But does that sound very intelligent to you?"
It didn't especially, but I didn't say so. (27-31)
OK, so Esmé has some negative stereotypes of Americans, but she's not entirely wrong, and the narrator knows it. He recognizes that his compatriots don't always act as they should, but still defends their despicable behavior, out of some patriotic sentiment.
"My first name is Esmé. I don't think I shall tell you my full name, for the moment. I have a title and you may just be impressed by titles. Americans are, you know." (43)
Again, we get the feeling that Esmé doesn't think that Americans quite understand the English and their culture – and she's probably kind of right, albeit in a ridiculous way.