That's possible! When a pup is small, you can tell if they've just eaten a big meal! But make sure he's been wormed, too. Most puppies have worms, and I've known breeders to lie when they say the litter's been wormed already!
Edit: forgot to add, it's not unusual for shepherd pups to have white markings on their chest, bellies or feet. These sometimes fade out as the pup gets older, and DO NOT mean the pup isn't purebred!