Yep. (Or as Yvain suggests, give a question which is likely to be answered with a bias in a particular direction.)

It's not clear what you can conclude from the fact that 17% of all people who answered a single question at 50% confidence got it right, but you can't conclude from it that if you asked one of these people a hundred binary questions and they answered "yes" at 50% confidence, that person would only get 17% right. The latter is what would deserve to be called "atrocious"; I don't believe the adjective applies to the results observed in the survey.

I'm not even sure that you can draw the conclusion "not everyone in the sample is perfectly calibrated" from these results. Well, the people who were 100% sure they were wrong, and happened to be correct, are definitely not perfectly calibrated; but I'm not sure what we can say of the rest.