Show the systemic change you made, not just the test you added. One new test case is a bandage; a process improvement is a cure.
Best answers show accountability and systemic thinking: how was the bug missed (gap in test coverage, untested integration, edge case), how it was detected in production, the impact and resolution, and the specific process or coverage improvement implemented. Look for root cause analysis, not just adding more tests.
Reveals quality mindset and accountability. Every QA professional has had bugs escape. The question is whether they analyse why and improve the process. Red flag: blaming developers.