"The adult wizard" was changed quite a while before the most recent round of retcons. Most of the other changes I can understand, even the removal of Ghostbusters, but this one seems completely indefensible. He's listing species that are dangerous, so it makes more sense to use a biology-type word like "adult".

And as Quirrell is perfectly open later on in telling everyone that he believes Harry wishes to become a Dark Lord, and also that he still wishes to teach Harry how to defeat his foes, there's no reason for him to put on false airs and claim that all the students present will have Dark Wizards as their enemies. He even took "Defense Against Dark" out of the class's name for crying out loud!