Well, I heard it's rather... controversial, to say the least.
[1] https://www.amazon.com/Hundred-Together-Complete-Volumes-Dve...
I am not saying that the book is not serious. It gives a valuable personal perspective of important historical facts. But it should not be used as a source of factual data.
I think you are confusing him with Putin, who actually said that. He said the cheka was mostly jewish. Which is correct.