I"m confused. You adopted? From a rescue? Shelter? Or you bought a puppy for a breeder?
If you bought a puppy, have you spoken to the breeder?
If you exchange money for a dog it is a purchase whether it is from a rescue or a shelter or a breeder. You bought a puppy.
If you insert a puppy into your family as a family member and prefer to think of that as an adoption, then it is an adoption whether the puppy came from a shelter or a rescue or a breeder.
So, let's not get side tracked about the real issue here.
10 pounds is small for an 11 week old puppy. But it is not out of the ball park. First check your paperwork and make sure there is no misunderstanding, what was the date the puppy was born?
Next, some puppies just grow faster than other puppies, some lines mature quicker -- and quicker is not always better. The pups that grow very big, very fast often have structural issues as they mature.
The smallest puppy I think I have let go was 8 pounds at 8 weeks, and she had a rough start. But, others have had pups as small as 5-6 pounds at 8 weeks that have matured into seventy something pound dogs. It does not indicate there is anything wrong with the dog.
In my first litter I had a pup that was born significantly smaller than the others, and grew at a slower rate than the others. I gave him to my folks in hopes that he would be a smaller shepherd and easier to handle for them. Nope, he just never seemed to stop growing. His ears would shoot up, and his tail would brush the ground, and then he would grow several more inches. He ended up being the largest in the litter.
Another litter of 10 pups had 4 females. The two visibly larger females went to their homes first. I kept the smallest. I started puppy classes at about 10 weeks old with the owner of one of the larger pups. By the time the class was over (six weeks), my puppy was bigger than hers.
When the vet looked him over, did he find anything wrong? Was he underweight?