The full quote is "Let me start by saying that unlike Mr. Shaw, I am not a writer. I'm an engineer. Thus, this will be written from that perspective."
By implication, Zed's book is not written from the POV of an engineer (otherwise why would this be worth noting in any way shape or form? The topic under discussion is already software engineering).
That is not the implication that I took from it; as I read it, this is an apology of sorts that the critique is not informed by the perspective of a writer.
His own words, strictly read, imply that:
It doesn't imply anything either way about Shaw being an engineer.