I applied for a more entry level software position at Jane Street, and while I would have failed the interview regardless, I had the same experience where the HR person had no idea what the interview was like.
They assured me I'd be required to write OCaml, so I spent the weekend brushing up, and that I should bring my own laptop prepared with whatever development I wanted to use. In fact it was a couple "whatever language you want" questions using their floating interview laptop, which threw me off a lot. But like I said I would have failed anyway, it's the hardest interview I've ever had.
They assured me I'd be required to write OCaml, so I spent the weekend brushing up, and that I should bring my own laptop prepared with whatever development I wanted to use. In fact it was a couple "whatever language you want" questions using their floating interview laptop, which threw me off a lot. But like I said I would have failed anyway, it's the hardest interview I've ever had.