Unless there's an explicit rights assignment for each instance of a work, software tends to be not considered a work for hire based off of precedent. A statement of all software work done for the employer by the employee won't cut it for the company either- they have to explicitly delineate the work the person does for you as an employee, and if it changes because of role change or line of business change, they HAVE to give you a new agreement or that clause usually gets thrown out if it goes to court as it's not presumed to be a work for hire except for a narrow range of things considered literary or artistic works.
Typically, you'd have to go to court to sort that sort of mess out, so most people don't dicker over the code- even at a game studio.
Having said this, we need to see if we can find the publisher's management or Les Bird's employment agreement before forging forward with the code he's providing on his website.
It's not out of the question, but it's forbidden fruit for now.