I think if we were utterly reliant on our senses to perceive reality, this would be a good argument in favor of realities ultimate inaccessibility. But we can actually reach beyond our natural senses to see things like microwaves and radiowaves.
The question is now: What else is out there that we haven't been evolved to perceive? In a way, most of the really useful science of the past several centuries have been finding new ways to discover those aspects of reality that are hidden to our primitive primate brains.
The argument he's making isn't about 'philosophical reality' as much as it's about conscious reality.
"Assume your fitness function is correct. Now assume it doesn't match reality. Therefore, your fitness function is incorrect, and thus fitness functions are useless."
My that seem like BS. I can't quite figure what on earth the argument is supposed to be but too much or too little water being bad for you sending "truth to extinction" just seems nonsense. Maybe it's some kind of late April fools joke?