I believe it's just him alone, but you know what's the problem if you do the 3D modeling for him? He has to describe what he wants exactly, then it's most likely it's not perfect, so you will have to recreate the model, or you may even totally abandon the project which means that he has to do it himself anyway. Also there is a lot more that can go wrong when you work with multiple people and thats why most developers like to work on their on. Even though I don't know this developer personally I think he want's to do it all by himself (or the team that he is in right now)