@HarmlessDave I doubt even that. I think the author's personal experience is just interacting with GMs as a player. There are no mechanics or terminology that would make me think "oh yeah, only a GM would know that" - all details about GMs in this novel are things that regular players would either know or assume about GMs.
But I do think that there is some novel balancing as you refer to it (see my answer to endoftheline).
@endoftheline Well, you're generally correct that you don't usually convert your regular player character to a GM. I don't think most companies would allow you, and even if they do, you probably wouldn't want to do that either, since keeping your regular character as-is would probably allow you to go back to playing after you quit your job as GM (which, as I said, is usually a part-time job so I doubt many people would turn that into a life career). In that hypothetical scenario where you convert your player character into a GM then once you quit your job it's completely gone.
Still I wouldn't call it an error - I'm pretty sure the author knows or at least assumes nobody converts their player char to GM but wrote that anyway because they wanted the protagonist to have access to all sorts of gear. If it were a new character, the protagonist would only have GM gear, which, depending on the game, is either completely "broken cheat gear" or purely cosmetic, nothing in between.