Assuming your interpretation is correct, that this is a not just a fact-based conclusion (a prudential judgment), it still doesn’t mean the Church has erred. See my earlier post where Cardinal Ratzinger speaks of the degrees of certainty and that doctrines in the Catechism contain no more weight than what they already possessed.
In this case, this entry in the Catechism is drawn from a random address of Pope Francis. It is not a definitive, irreformable judgment (so it is not infallible). The contrary position has not been definitively condemned. Holding it does not exclude from the communion of the Church.
Because of all that, Pope Francis could simply be wrong. A Pope being wrong does not mean the Church has defected from the faith. And, given the controversy, his opinion has clearly not been received with docility by the whole Church (contrary to centuries of unanimity to the contrary position), which is further proof that the Church has not defected.
If we were to apply it a theological note, at the very best it would not even be “probable” since there is more weight against it than for it. The denial, therefore, would involve no sin.
Anyway, this is all assuming your interpretation. Given the history of this passage in the catechism, and the history and justification given to this change, I think it should still be interpreted as a prudential judgment subject to revision as the circumstances change.