1. Here's why it's illogical to be a fence-sitting agnostic
2. Here's why it's illogical to posit God as an explanatory philosophy of the universe
3. Here are some specific problems with common theist arguments
4. Okay, now that we've got all that out of the way, here are some interesting theories on how things got to be the way they are
In other words, the part of his book that you single out is the part that he attaches heavy disclaimers to. The fact that you chose to focus on it suggests to me that your belief that "it's impossible to know for sure one way or the other," is even more of a gut-feeling assertion that you're accusing him of.
(I'm not sure if you mean "design patterns" in the general naming of abstractions sense, or if you mean Gang of Four specifically. If the latter, I'll point out that many of the GoF patterns really aren't relevant to Javascript unless you're writing it in a very OO style)