Australia is a big place, you should get a little more familiar with it when you want to think about the scope of this fire. It's not the size alone that's unprecedented (because as you point out that's obviously not true), it's the fact that it's so big, so early, and in such a weird spot. Very new for that area. If all of the east coast of the US burned and we shrugged and said, "Eh, California's were bigger in '88" it wouldn't be a meaningful comparison at all.

Quicky edit: All that said, I'm no expert either. I think we're both more or less parroting sources, so feel free to respond with new info :)