Why does Brandon have to respond to a 3rd party allegation that he owes someone money? If I start a post staying "someone told me FPS_Russia owes someone money" do you then need to disclose every single person you owe money to along with the specific details of each arrangement? NO.
If a 1st party comes on and accuses you of rolling them then I would expect a response.
Just because Brandon is a "public figure" doesn't mean he is obligated to divulge every detail of his personal life. And he certainly doesn't have to comment when the questions come via a telephone game of unreliable proxies.