literally, it's "all the world" I think that should be accepted, my understanding is that saying "todo el mundo" is a hyperbolic way of saying "everyone" like here the person seems shocked at how many people were invited (hence the exclamation points) But I'm not a native speaker, so I could be wrong.
"Everybody" does not mean all the hands and legs and heads and pancreases and other body parts; it means everybody. In the same sense, todo el mundo is not used for the whole world; it's used where an English speaker would say "everyone" or "everybody". If you really want to talk about the whole world, use el mundo entero.
For something completely different, I'm glad the textual portion had the exclamation marks to clue us in. This speaker sounded flatter than a pancake which would have me inclined to use the good old period. Thankfully, unlike in a real classroom, Duo cares not about punctuation except to warn you when you get accents wrong. (reported 2019/12/15)