The way I understand it, they are saying that in certain areas the Koalas are now absent and therefore are not part of the ecosystem any more, and that means they are no longer a functioning part of that ecosystem (so, "functionally extinct in the Australian landscape" or whatever their phrasing was). That isn't what functionally extinct means of course, but I think that's what they are trying to say. I also think it is deliberate on their part to create a more scaremongering atmosphere to further their cause.