In the way that not everyone is convinced that it is genuine. You and I may be, but not everyone is. So the jury is still out, like it or not.
Upon listening to it again now after a good night's sleep or two, I am 99.9% certain it's genuine. I would like to hear more of this bootleg, but I agree that something like this would be very hard to fake. My initial idea was that it might be one of those fanatical Brazilian tribute bands. However, the weak spot of those bands is always the Bruce impersonation, and I have never, ever heard anyone nail him like that.
I think you're overestimating what can be done with digital voice manipulation. I also think that maybe you're putting a bit too much faith in testimonials of people trying to remember a specific night 40 years ago. Memories can be clouded by subsequent events, and since BITV was never played again, it's easy to forget during a 200+ date tour that it had been played once. To most people involved, including the band, this is something of little consequence, which is why they would just forget about it. Human memories are a highly unreliable source.