There were two waves to the Spanish Flu. Wave 1 started like the standard flu - it was mild, hitting mostly the old and ill, and not terribly deadly. Wave 2 is when it mutated, spread like wildfire, and killed 2% of the world population.

From what I can tell they aren't completely sure what happened here. One theory I read is that WW1 reversed the trend of what happens with flu: if you had mild symptoms, you stayed on the front line. If you had severe ones, you got shipped back home on crowded trains and ships. This is in contrast with regular life - if you get a mild flu you still go out, but with severe flu you tend to stay at home.

I don't think Corona virus will turn out this way. But it also doesn't seem exactly correct to say Corona virus isn't like the Spanish flu. There's lots of possible outcomes as it continues to go global. We just don't know.