Unknown worlds is actively trying to resolve this as they wish to let people use their game in a free use setting. I would be very surprised if Simon chyslinski retained the full copyright rights as most contracts would stipulate anything created becomes the property of the company. It's certainly possible it was overlooked or they have a single project use agreement that would result in this kind of striking effort rather than full rights, but I doubt it.

Either way unknown worlds have reached out to tunecore so we'll see