I'm not a breeder by any means, but in response to your question I believe it's a little of both.
Hedgies, like people and all other animals are born with their temperament. Some naturally will be more friendly than others. Having good temperament in the parents can lead to good temperament in the babies, but it does not ensure it. Sometimes our little ones are just born a grump.
However, by being handled from such a young age, as well as spending the quality time that breeders do with the young ones this most definitely add can to better temperament. The more they are handled the more likely it is for them to have a better temperament. This is also why it is suggested to spend around 30-45 minutes of bonding time or more a night with your hedgie because they more they are handled the more likely it is for them to come around.