Comment by somenameforme

That's a bit misleading: "The outbreak did not originate in Spain,[49] but reporting did, due to wartime censorship in belligerent nations. Spain was a neutral country unconcerned with appearances of combat readiness, and without a wartime propaganda machine to prop up morale,[50][51] so its newspapers freely reported epidemic effects, making Spain the apparent locus of the epidemic.[52] The censorship was so effective that Spain's health officials were unaware its neighboring countries were similarly affected."

In other words other countries were effectively censoring it out of existence owing to WW1. Spain didn't have such censorship/propaganda going on, and so was seen as the epicenter (even within Spain!), even though it ultimately wasn't.

[1] - https://en.wikipedia.org/w/index.php?title=Spanish_flu&oldid...