I answered that I would get PM to clarify the requirement to see if it is a bug or not since PM is the owner of the product and expert with client and requirement. It seems that the answer is not good enough. I was asked again what if I disagree with PM, too. I answered that I will let PM make the call if I already provide all the facts. I feel that they wanted someone to fight the nail about defects that I don't agree with. It is ultimately about the clients' requirements and use cases.