They may have eaten some of what the prey had it its stomach, but that would not be human fruits or vegetables. Anything you give your puppy beside a good quality puppy food that follows AAFCO recommendations is likely to worsen his health. A young small breed puppy has a small stomach, too, so any amount of extra human food is going to make a huge impact on how much of the balanced puppy food he eats. There are many excellent choices available now, canned and dry. Royal Canin, Eukanuba, Iams, Hills.
And Purina all make very good foods that have proven time and time again to be great sources of nutrition. Please do not get taken in by the ‘natural’ food gurus and pet food advertising propaganda: they appeal to your emotions and to what a human should eat rather than looking at actual scientific data on what is good nutrition for dogs and puppies. Your pup is growing now, and making sure his diet is only puppy food at this stage is crucial.