I don't think tptacek actually presumes everyone is American, he is simply using a figure of speech which is local to America. As an American, my impression is

I don't think tptacek actually presumes everyone is American, he is simply using a figure of speech which is local to America. As an American, my impression is that the phrase "good red-blooded American" derives from the Cold War, or possibly earlier. For example, during the anti-communist movement of the 1950's, the term would be used judgmentally to distinguish from those who might be "pinko commies". C.f. "better dead than red". Since the communist threat has obviously subsided, today I would interpret Ptacek's use of the term "like any red-blooded American" as both calling to mind a shared experience which many of us have had (growing up in America, reading Schneier's Applied Cryptography), as well as reminding us of the risk of failing to think beyond it.