I had no way of knowing they knew each other. It wasn't listed in the guys game description and I don't follow either of thier social media. How in gods name would I have figured out they knew each other?
Maybe perhaps, i don't know, simply ask? Politely? I mean, i hate people who steal other people jobs but if the developer is using content from another person, either he know that developer, he asked for permission or he stole it, and oh surprise you obviously have no way to know which one and simply assumed it.