Confluent Developer Advocate interview questions

Interview process was pretty straightforward. I received a call from a recruiter for a phone screen, then was told I'd move forward with the hiring manager. During both of my calls I specifically asked if there were any concerns about my background that could negatively impact my chances for this role. At no point did they raise any concerns until the day I was rejected because I didn't know Kafka. I feel I could've addressed this concern during the interview if given the chance.