Only 85% of the population owns a smartphone, I thought for sure it would be higher than that

The math contributes some to this. Let's say the correct answer is 1%, and out of ten people, 9 of them guess 1% and the other guesses 51% - that one guess shifts the average from 1% to 6%. And if it's 1%, then there's no room for people to underestimate and bring the number back down, and the same is true of numbers close to 100%. The numbers closer to the middle don't necessarily mean that people were more correct on an individual level, but that some people overestimated and others underestimated and it came out closer to the right number. The graph ought to give information about the spread of errors and not just the raw average.

the proportion who have at least a high school degree: estimate 65% vs. true 89%

the proportion who have an advanced degree: estimate 37% vs. true 12%

So basically what they guess is ±⅓ has no high school diploma and another ±⅓ has an advanced degree, while in reality ±^1^/~10~ doesn't have a high school diploma and ±^1^/~10~ has an advanced degree.

Meaning while in reality 77% does have a high school degree but not an advanced degree, the estimate is that only 28% does.

Hold up.

83% have a driver's license but 88% have a car?

So 5% of Americans either have a car for the hell of it, or they drive without a license?

And there's only 3% that are atheists? More people drive without a license than are atheists?

Excuse me?

If these numbers are correct, the US is more fucked than I thought.

The actual problem is that if you show this data to the respondents, they wouldn't change their answers.