If said Chinese ambassador wrote a book that was also sourced (like this British ambassador's book is in a fair few places), their claims aren't disputed by any factual evidence and is generally corroborated by historians, I'd be inclined to believe them yes.

I wouldn't expect said ambassador to have a scientific study backing up every single sentence in the book. If he's writing about his experiences, that can be a valuable perspective on things. I wouldn't treat it as gospel necessarily but I can still apply critical thinking to ascertain whether or not they're a credible source.