I have never met Brian and know nothing about him except for what I saw in the movie and in the "Wiebe gameplay dissection" video, but a 2002 KS claim is extraordinary, for a number of reasons, and as we all know, in his case there's a lot of personal baggage and "politics" around the question of KSing and when he did it.
This is one of a few particular instances where extenuating circumstances are ringing alarm bells for me.
I'm gonna be blunt: I have serious doubts Brian KSed three years before the KoK FS footage was filmed (and, conveniently, a year before Steve Wiebe's first TG submission). Literally everything that Brian says and does in the movie would strongly suggest that he was not capable of KSing at the time, or having a game that went 30K shy of Billy's record. In the words of Brian himself, "nobody had gotten close to that."