None of this was called into question as far as I understand.
The problem in the initial critique was that the author of the book misattributed the epidemic claim to WHO. He subsequently admitted that he misremembered and really it was the CDC. He provided a source to back this up on the blog.
The poster above then seemingly called the veracity of that into question, based on a brief investigation.
This prompted me to do my own investigation, because I wanted to know what was true after all. Up to that point I was unconvinced of any malicious intent on the author's part.
And it turned out that the author was not lying. That's all.
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As for the use of the word "epidemic" I agree -- it might have been an exaggeration/hyperbole or colloquial use (a bit out of place then) on CDC's part. This is probably why they eventually changed it to "problem".
The article was online however for close to 6 years under the original headline and even though it was updated long before the book was published, I would not hold it against the author, because the book was most likely written over a long period of time.
That there are mistakes and errors, shows to me that it might have been a bit rushed towards the end.
None of these significantly alter the validity of the message and the author admitted and corrected them -- a revised edition of the book is apparently in print. To me this means that he cares.
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On a personal level, I feel the message of the book comes from a good place. It does point to real problems that are systematically overlooked/ignored/marginalized/ridiculed and it is completely plausible to me that taking steps to fixing them might significantly improve society. Some exaggeration might be in order.
I read the book and the information did contribute to substantially improving my life. I verified some data in it by self-experimentation. It is harmless and scientifically-sound enough to offer people looking for solutions to their sleeping problems.
For the unfortunate these are absolutely not trivial and incomparable to bad posture. Bad sleep can make one's life absolutely miserable. A lot of miserable people makes for a miserable society.
Hope you sleep well.