From GameGirlAdvance:

I’ve claimed that Americans tend to assume that everyone else is also an American. At first glance, it might seem this quote is an argument against my claim, but actually it’s an argument for it. Notice how the author assumes that given “Tim” is a Canadian-only piece of information, anyone who speaks English and doesn’t know about Tim must be American. As opposed to being British, Australian, African, Chinese, German, Arabic, etc.