Earlier quoted context omitted.
To be purely pedantic: Spanish flu was only called that because Spain was the only large country reporting accurate infections and deaths. It ought to have been named American flu, since that's were it originated, but the US was intentionally underreporting (war time rules and all).
Yeah. That’s the history, and widely understood. At least in Europe (incl. UK) Only a fool would think that it was because the Spanish we’re dirty or adversely affected.
Nationality-based idioms and names (and stereotypes in general) are on a subjective spectrum of offensiveness, IMO. "Irish exit" and "French disease" can be benign to one individual, but offensive to another.