Because the title of the thread was not misleading when it was first posted? Whether BGS damaged his cards or not, it’s entirely reasonable in that moment of anger for a customer to respond negatively given the lack of communication.
Why is it your prerogative to step in and tell him (on multiple occasions) to change the title of the thread? BGS does not need defending from an unaffiliated party, and it’s none of your business to tell someone how they should feel when they have received poor service. That is something a company employee or brand ambassador would do.