Jane Street are big players in the OCaml community (they build/maintain what's arguably the defacto standard library for the language - Jane Street Core) and apparently make a lot of money being good at what they do; so I'm inclined to believe them.
Devils advocate: they're not doing anything better than anyone else in the market and they don't make a product. They're very invested in their ecosystem which is only as good as they make it because they have a very quiet, well funded (pun intended) echo chamber and a lot of spare cycles to maintain a STDLIB on top of their actual business.
