I suppose not; I haven't read the book, and only recall reading the article a while back. But the man's position in the administration at the time he chose to leave lends to the credibility of his claims, both from the perspective of his level and his regular interactions with Trump. This was no coffee boy.
I read some stuff on this in the last few hours (well, mostly over lunch time). I came on this which, I cannot say is true or not. But apparently this individual knows what she is talking about.