That is how our server at Le Cellier described it. I am not sure why they would use duck gravy, they don't have duck on the menu that I can see. They don't have any items with beef gravy either.
What I think happened is that a lot of people have asked for Poutine. So they decided to put it on the menu. They really didn't think the logistics of it all through very well. But now they can tell people they have it. It is also rather cheap, only $4.49. I would expect real poutine at WDW to be closer to the $6 range. I don't know how big the serving is.