Even though you don't work directly for DevOps in your role as a site reliability engineer, you interface with them daily and therefore need to be familiar with their process and the tools they use. The Google interviewer will ask you this question to confirm your knowledge and determine if your perception of the process and tools is similar to the ones they use in their organization. You can align your answer with the processes of the interviewing organization by carefully researching their operations. Sources for this include Google's website, the job description, and both current and former Google employees.