Citadel Securities Phone Interview [What to expect?]

I worked with a headhunter to get an interview at Citadel Securities. He said he submitted me for quant dev/research, and I have an interview soon. I asked what role I'll be interviewing for at Citadel Securities, and he said that it depends on how I interview. So I have no idea what role I'm interviewing for, which seems strange? Is this normal?

It could even a plain software engineering role for all I know.

I also got the name of the person interviewing me. I thought about Googling him to see if I can tell from that what role I may be interviewing (e.g., if he's a quant and interviewing me, it's probably a quant role), but this person has no LinkedIn or any other searchable information..

Anyways, does anyone know what kind of topics I should expect? Since CitSec is an HFT firm, I've had people tell me that I could be asked concurrency/multithreading questions in C++ in addition to standard Data Structures & Algos, and math questions.