The costume designer didn't make the designs, he made the costumes... The designs were LFL intellectual properties first, so I think he's really not got much of a case there against LFL. At least if I'm reading that correctly that's what I'm concluding.
It's all about the intellectual property, not whether you were contracted to make the first one based on that intellectual property...
It's like an ILM model-maker mass producing X-Wings and selling them for $5000 each as he makes them like he did in the 70's. That doesn't make him the X-Wing creator, just the manufacturer. So I don't think this guy's got a leg to stand on.