In some cases this is "free for non-commercial and I consider it commercial if you have a revenue of >x$ from the game itself"
In other cases it is "free for non-commercial, and I consider it commercial if you have a donate-button that gives you 1 cent per year on the website where you give away the game for free".
In other cases it is "free for non-commercial, and I consider it commercial if you have a donate-button that gives you 1 cent per year on the website where you give away the game for free".
In your case, the product is the game, which you are not using for financial gain. You are using the separate product of your soundtrack, which does not contain any of the RPG Maker assets you're concerned about. So this would only be a problem if, as Andar describes, one of the authors took it upon themselves to make up a more draconian restriction.