Optiver Software Engineer (C#) interview questions

I apply mid/senior software developer(Shanghai) on LinkedIn. A few days later, a HR contact me on LinkedIn and we have a short phone chat the next day. She asked me why I want to move and go through my past working experiences. She seems don't satisfy with my answer about why Optiver. About twenty minutes later she said I was not suitable for this role which requires a full understanding of the whole trading system, performance tuning, etc. I'm really excited about the coming technical interviews. What a pity!