I think you are mostly right, only that they can distribute the binary since they have the rights to do whatever they want with their own code. If I fork it I

I think you are mostly right, only that they can distribute the binary since they have the rights to do whatever they want with their own code. If I fork it I think I could add a new proprietary dependency and release the code for it but once it is built the binary would be unsharable as you say. What I was trying to say originally is that if I was writing proprietary code I would not be able to add a gpl library and distribute the binary but I could do it the other way around.