Perhaps because Neely's pro-Lincoln bias is well known. He's also one of the leading deniers of Ben Butler's colonization meeting in 1865 despite conclusive evidence that it happened.
So what facts did he get wrong?
Without having that particular book on hand, I couldn't tell you. It is however hypocritical to write two books on civil liberties in the two different regions of the civil war, bash one side for supposedly violating them, and then praise the other side for doing the same thing.
And what makes you think he does that?
In his work on Lincoln he is critical, but places the abuses in the context of the war.
As far as I can tell from the review of the book on the Confederacy, he does likewise for Davis.