The series of tweets for me just wasn't illuminating and I didn't get what the actual 'paradox' was given the graphs. But my issue was more that the graphs weren't clear in pointing out what I should be looking at.
If anyone's impatient like me, this example from wikipedia helped me get it:
> For example, a person may observe from their experience that fast food restaurants in their area which serve good hamburgers tend to serve bad fries and vice versa; but because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation.
Wikipedia was much clearer for me, https://en.wikipedia.org/wiki/Berkson's_paradox , but ymmv of course.
Another good statistical foible to be aware of along with Simpson's.