In the earlier section 'Key Characteristics of Distributed Systems', it reads, 'By definition, availability is the time a system remains operational to perform its required function in a specific period. However, in this section it reads "Availability means every request received by a non-failing node in the system must result in a response."

One of these is a metric and the other is a non-functional requirement. This is a big difference! It's exactly the kind of difference that an interviewer will notice because it telegraphs that the candidate doesn't truly understand what they're talking about.