> It's so bizarre to me when North Americans proudly claim "Viking ancestry", rather than Scandinavian.

Where did you hear it? I am sure at least one out of hundreds of millions of Americans claimed it. But you know, we have people who think the earth is flat, as well. But by that token one can take any dumb thing someone from a large group said and sort of say “why do all X say this one dumb thing”

At least from my experience I only heard people claim Scandinavian ancestry. Or even more specifically a country like Norway or Sweden for example. Places like Minnesota or Wisconsin have a lot of that.