My initial thought was a systematic misinterpretation of the question (% of population vs % of cases), but you never know with people, numbers and statistics.
That still doesn't explain it. They thought 20% of people caught the virus, and 9% died. Even if you think they understood the question as how many people
who have caught the virus have died, they are still orders of magnitude off. No matter how they interpreted those questions their beliefs are very disconnected from reality, but you can find the actual numbers published on dozens of websites. It's so easy to look up and find out how many have actually died.
I know people are bad at math, but this is some seriously elementary math. I don't even understand how someone can function in life without being able to perform such simple math. The study says it's nationally representative, so I assume they aren't taking these polls in some kind of care home of mentally unfit people. Apparently it's just free range mentally unfit people that are representative of our actual population.
Or maybe these people just don't follow anything and were not prepared at all, like if you asked me how many people die from leukemia each year. 100? 1,000?, 10,000? I have no fucking idea, and I spend exactly 0% of my life worrying about leukemia, even though I'm aware of it and I know it kills people. Still, if I was part of a survey and had to give an answer it would probably seem completely disconnected from reality, because it is and would just be made up on the spot.