I don't see how it could be random, regardless of whether it is an actual language. Humans are famously terrible at generating randomness.
I wouldn't assume that the writer made decisions based on these goals, but rather that the writer attempted to create a simulacrum of a real language. However, even if they did not, I would expect an attempt at generating a "random" language to ultimately mirror many of the properties of the person's native language.
The arguments that this book is written in a real language rest on the assumption that a human being making up gibberish would not produce something that exhibits many of the properties of a real language; however, I don't see anyone offering any evidence to support this claim.