If I understand correctly: Grey-Poupon started in Dijon and the Reitzel brothers in Switzerland first imported it. Then they started to make it in Aigle (Vaud), Switzerland, and the French company kind of disappeared. Not sure, but Grey-Poupon is probably still made in Aigle.
This came as a surprise. I had no idea. (Not that I thought it was made in Dijon proper, but at least in France.)