What a beautiful boy! I can see why they labeled him a Rottie, but from the information you provided (double dew claws) and the image – I am going to say he is a Berger de Beauce (formally known as a Beauceron) mix. It is possible he is even a Beauceron x Rottie mix. Beauceron’s are also known for the double dewclaws on the hind legs!
From Wikipedia: “The Beauceron is a guard dog and herding dog breed falling into the working dog category whose origins lie in the plains of Northern France.”