There's a difference between the authenticity of the text and the question of whether Bakker is the originator of the posts. If the text was cut-and-pasted from Bakker's work then it would sound like Bakker because he wrote it.
The issue of needing access to the email address makes it very likely that it is Bakker. But if all he does is post material he's already published elsewhere then it might as well not be.