Translation:This airplane is big.
Disgruntled Britons/Australians/etc have a clear model to follow ;) I am surprised that Duolingo doesn't just alter the hints and word boxes in accord with IP address to preempt any possibility of such a potential competitor putting a dent in its non-US market share. They already handle most spelling differences and common word choice differences automatically. I don't know why they haven't taken the obvious next step.
Big and Huge are different in the same way that Expensive and Extortionate are.
One is an (usually unexpected) extreme version of the other. You can see this in the kanji:
Both contain the kanji 大 meaning "big" and 巨大 is used to show when something is not just big in general but larger than it's expected to be: 地震 for Earthquake 大地震 for Major Earthquake 巨大地震 for Megathrust Earthquake
So DuoLingo is trying to teach you big - not huge. It's not retarded, it's just being specific. If it wasn't then you'd be learning incorrect Japanese.