It's a neat org. Hearing voices isn't really uncommon and doesn't mean there's anything wrong with you and they're trying to raise awareness of that. Check them out. Hearing voices, outside the context of serious mental illness, is just one of those weird human quirks that some folks have like the cilantro gene or ear wax variations.
Yeah, my best theory is that when someone yell's "Tiger!" And you hear "Tiger!" Then you don't get eaten because you were warned and hid from the tiger.
And when you have a hallucination of someone yelling "tiger" you still don't get eaten.
But if someone yells "Tiger!" And you don't process that in to the word "Tiger" then you get eaten.
So I think, maybe, that it's been better for us to be to hear something that is there than not hear something and there's a bias towars interpretting sounds as voices. Because maybe there's a tiger.