Pep had control over their last game of the season, the game which decided their fate, it was in their hands. You couldn't change one other result somewhere else and change their fate.
So if Palace had lost to Cardiff, would you then say he had "sent us down". How can he have both "kept us up", and "sent us down" with the exact same set of results. It was out of his hands. He did neither of those things.
If Palace had lost to Cardiff, we'd be preparing for Championship football. You can't say CH "kept us up" if the results he achieved meant relegation if not for another result completely out of his hands.