They didn't say they were profitable - they said they were cash-flow positive. And if you look at the cash flow statement in the S-1, they were indeed cash-flow positive in 2019.
It looks like much of the difference comes down to stock-based compensation. This doesn't cost the company any cash, but under GAAP, it has to be recorded as an expense. (IANAA, so take what I say with a grain of salt).
Presumably the employees are working below-market in exchange for equity, so the company is not really profitable yet - it's sort of "ramen profitable" in that it's profitable if you don't count the full rate of the workers' time.
