Today I learned that prior to testing the first atomic bomb, Manhattan Project physicists made bets on the whether the bomb would ignite the atmosphere and vaporize Earth.

Exactly, what you just summarized is the result of the calculations they did to determine if the bomb could trigger a fusion chain reaction. But they didn't just know that, because you can't just intuit that sort of thing. They did the math to make sure that it couldn't happen. Which is why the verb "worry" is appropriate when taking about why they did the math in the first place.

My point was more though that you bringing up light elements not being fissile is completely the wrong explanation. They easily knew a fission chain reaction wasn't possible, that was never a question. The question was if a nuclear blast could trigger a hydrogen fueled chain reaction in the atmosphere (or in the sea where hydrogen is much denser). It can't, but they didn't know that until they did the calculations.

/r/todayilearned Thread Parent Link -