We know for a fact that they put the project on hold for half that time, and that less than 15 devs worked full-time on it, and the salaries certainly didn't amount to $100K/year.
I've got my own theories about how they funded this, but $100k/yr for an entry level programmer is
low for Boston. Remember, that cost needs to include health insurance. It's probably more like ~$135k minimum per developer, plus rent, utilities, overhead (admin staff - that have health insurance as well), etc.
Codex cannot into running a business. I know some of these values seem crazy to those outside the US, or hell, even to those living in the southern parts of the US, but that's the market. A 2 bedroom, 1 bathroom apartment near boston will cost you ~2.5k+/mo,
easily. Shitty food is $12/plate. Welcome to the north east!