It's cause the guy was a dick about it... He was correct, but the way he communicated it to the medical community was rude which is why it wasn't adopted earlier.
So they had a cry and people died because they had their fefe's hurt when the smart man correctly identified their habits as neanderthalic? Well if that wasn't proof enough, this sure doesn't make them seem any more capable or less moronic.
No he had no reason or justification as to why it was happening. He also refuses to do any experiment to prove he was right. That's why no one took him seriously because he sounded like a crazy person.