The illustration is not analogous. The first picture is based on the perception that centrists have of themselves, the second is the reality of that perception. It’s a metaphor. Humor does not always follow logic, crazy right?

This incongruity model can explain why older adults do not comprehend jokes as frequently as younger adults. Due to declines tied to the aging process, older adults may not have the cognitive resources needed to create multiple representations, to simultaneously hold multiple ones in order to detect the incongruity, or to inhibit the first one that was activated. Getting the joke relies on working memory capacity and control functions. However, when older adults succeed in their efforts to do these things, they typically show greater appreciation of the joke than younger adults do and report greater life satisfaction than those who don’t see the humor.

Interesting read on why sometimes we don’t get the joke.