If that’s a theorem, what are the axioms and permitted inference rules?
Strict formal logic might struggle to infer that those people even exist, let alone anything about the unobservable contents of their minds.
But I assume there’s no $10k on offer for generic skepticism, so the question becomes “What would be deemed valid and satisfying by the person posing the problem?”—which is a futile tarpit if they’re motivated to disagree.
Weird and not sure if it’s just me, but the frame with the video in it has failed to load in Firefox (seems fine in Chrome)
For anyone with the same issue, it’s at https://www.youtube.com/watch?v=qHpnWiBHHaU