The sense in which your (correct) belief that you are not a Boltzmann brain is justified (or unjustified) seems to me analogous to the situation with the green-glove copy believing that its unobserved glove is green. Justification is a tricky thing: actually not being a Boltzmann brain, or actually being the green-glove copy could in some sense be said to justify the respective beliefs, without a need to rely on distinguishing evidence, but it’s not entirely clear to me how that works.
The sense in which your (correct) belief that you are not a Boltzmann brain is justified (or unjustified) seems to me analogous to the situation with the green-glove copy believing that its unobserved glove is green. Justification is a tricky thing: actually not being a Boltzmann brain, or actually being the green-glove copy could in some sense be said to justify the respective beliefs, without a need to rely on distinguishing evidence, but it’s not entirely clear to me how that works.