This made me curious so I looked a bit into it. Seems that milquetoast as an insult originates from an old comic character of the same name, and it’s at least feasible (and perhaps likely) that said character was named after milk toast.

I spent a few months in Germany years ago, and “Americans” (Amerikaner) tended to be used to refer to people from the Americas (either NA specifically or NA and SA collectively) in my experience. If you wanted to say someone was from the US, you’d say something more like “aus den USA.”