Yeah, that does not surprise me. Americans are not always that great at global geography.
I'm not sure why that is. Of course the country is huge, and American culture is such a dominant force that it is not so hard to live your entire life and never learn much (anything?) about a relatively small city-state far away in Asia. If you've never met anyone from Singapore, this doesn't surprise me at all.
It still feels like something that the US should be better at as a nation, though.