An editor can shape your book and your sentences. A proofreader does grammar. Since writing about the entertainment industry, he would need a fact-checker from that realm, someone who knows about Arbitron and Desilu and Stalag numbers. Kind of like what Kellam DeForest did for Trek science.
I didn't have the budget for a fact-checker for my book, though there would be several knowledgeable folks about Satchmo who would've known the facts; and many more who can recognize a potentially-wrong fact and research it. I had to -- as best as I could -- recognize anything I might have gotten wrong, and double- or triple- check it. Even then, I am afraid some expert is going to instantly see something wrong, which will undermine the rest of it. One does what one can.
But with so many errors easy for knowledgeable readers to see, it certainly calls into question other facts and conclusions about which we do not know. Why don't some of you offer to proof or fact-check his next volume? (I think I already did upthread.) I'd do it for a modest fee; probably there are kind souls with time who could crowdsourcedly check it for him. Might be a nice IDIC-ish thing to do.