> The latter appears when analyzing subgroups gives a different result than analyzing the pooled data.

> The former is about correlations that appear in samples which are not representative of the general population, due to the way that those samples are selected.

You just said the same thing twice. Think about it.

For one you used terms like "subgroups" and "pooled data" and for the other "samples" and "general population". Those are the same things.

Then you used "[the effect] appears in" and in the other "correlations". Well, Simpsons paradox can also manifest itself in correlations. So you just said the same thing twice.