Welcome to YorkieTalk! It's really too bad your breeder let him go at 6 weeks, but at this point there is nothing you can do about it.
I would just suggest anyone reading this thread not to purchase from a breeder that releases puppies before 12 weeks. A LOT of development happens between 6 and 12 weeks, and it is vital that puppies stay with their moms until they are older. A puppy may 'seem' to be doing well at 6 weeks, but there is no saying what problems this may cause later on in their lives