Interviewers intentionally leave things ambiguous. They want to see how you handle it:
State your assumptions: "I'm assuming a read-heavy system with : read/write ratio. My design would change if it's write-heavy."
Ask when it matters: "The choice between strong and eventual consistency impacts architecture. Which does this system need?"
Decide and move on: Don't get stuck. "I'll assume eventual consistency. Let me show the design, and we can revisit if needed."
Ambiguity tests your judgment. Make reasonable assumptions and adapt when corrected.