Popper's is very specific about what exactly he means when he says he changed his mind, and what he is recanting. He adds only this: "How the theory of natural selection could be untestable and yet of great scientific interest ... My solution was that the doctrine [note that word well!] of natural selection is a most successful metaphysical research programme."
That is ... he is pulling the wool over your eyes, you confounded, self-made idiots, deluded by Darwinsism.
Just like Galileo under his breath ...
For another analogy, the saying "scripture interprets scripture" might be applicable here: wouldn't one want to look at the totality of an author for illumination of a controversial passage? (Some Roman Catholics might not agree with that principle, so your mileage may vary...)