[credit_guy]

You are most likely right.

I am personally bothered by the way it is presented as a "paradox", with the implication that it would have real world applications.

I have zero doubts that you can't improve the estimate of the US wheat yields by looking at some other unrelated things, like candy bars. Presenting the result as if it a real "improvement" is false advertisement.

On the other hand, if we look at related observations, then the improvement is not a paradox at all. Let's say I want to estimate the average temperature in the US and in Europe. They are related, and combining the estimates will result to a better result, to nobody's surprise.

[falseprofit]

Since when does “paradox” imply real world application?

In your last paragraph, what you’re describing is just inference based on correlation, which is unrelated to this topic.