Despite looking like a gambling website, the underlying system is a cryptocurrency exchange. With a separate cryptocurrency used as an oracle to decide (yes/no/later) if the yes or no side won. The site itself if pretty hands off with the actual financials. (though, they once did refund people when the oracle system resolved incorrectly)

I don't think this convoluted setup is enough to avoid US gambling laws, but it is important to keep in mind how it actually works.