You're all dead wrong.
Nobody* claims to be of "American Ancestry" on census forms. "American" is just the Census Bureau's catch-all processing category for all the written-in regional terms from within the US, whether it's "Baltimore MD", "Ohio", "Appalachian", "Southern White", "old Yankee stock", or whatever. The ancestry field on the longform census questionnaire is a write-in field, with relative little instructions on use given (see
question 10 at the bottom of page 4), hence how this happens for people who don't have a clearcut country to jot down. Also note that, no matter how many answers you give, the Bureau only processes the first two.
*well, maybe some people have taken their cue from the Census Bureau by now. But not anywhere near most of the people who show up as such on the result sheet.
