In payment disputes bank dispute resolution often requires a response of any kind from the customer to consider rejecting the dispute. In addition, the submitted forms/disputes often have nonsensical or no information on why the dispute occurred so you truly have no background. Lastly, disputes can be initiated by people without emails or just different emails so you have no chance to connect it to relevant support cases.

That's why he's curtly asking why the dispute was raised - yes in part to pressure the guy directly on his BS knowing he responds, but also because you need any kind of response to win disputes.