Not having watched most of his performances, I’m not sure why he picked 1917. If there was a “reason,” do you know it?
In any case, a friend of mine has traced the 1918 pandemic all the way back to a British encampment in northern France – in 1916.
So we could say that both “Spanish” and “1918” are inaccurate as to the origin – but they remain perfectly accurate as to where and when the explosion was large enough to first be noticed – and acknowledged.