https://www.spaceweatherlive.com/en/solar-activity/top-solar...
https://en.wikipedia.org/wiki/List_of_solar_storms#Proxy_evi...
Some of the accounts linked with those events are almost of biblical proportions. Red crucifixes on the sunset (associated with the 774–775 carbon-14 spike), sky serpents and so on.
The unpredictability of those events is a major point of anxiety by the way. We don't know enough to predict when the next big one will hit, and modern society has never seen one (the Carrington Event being the closest match, but still timid compared to the proxy evidence we have for what a strong solar event could be).
The table you cite goes back to the 1960s. The weather in the article occurs about 100 years before that. Not recording an S5 event doesn’t mean humanity has not experienced one.
Whether it’s worth preparing for is another issue entirely.