Illumio Data Engineer interview questions

The interview process was quick and the recruiter was helpful throughout the way. I had a phone interview with one of the engineers. I was then asked to do a coding challenge which was fairly easy but I somehow did not pass. I asked for a feedback and they were kind enough to provide me one -- nitpick on minor optimization that I chose not to do as a tradeoff. Makes you wonder if they are screening for basic CS fundamentals or looking for ninja/unicorns for a junior role. I got a sense that they are looking for Ruby developers.