Uh, I don't know but the quantity of writing is certainly WAY more in Adv. than it is in Extension.
If Adv. you're required to write five different papers for your exams, ranging from 800-1200. In Extension, you write two papers. ranging from 1000-1500.
So if you compare, Adv has way more writing to do.
Difficulty wise, I say that Extension is more specific with its questions - and what the markers are looking for. Not only that, you have to remember critic's opinions on texts alongside with quotes / techniques etc.
IDK why your teacher said that, since Ext. only has a creative and essay element. Plus, don't forget the unseen in Adv!