It doesn't seem to be getting any bigger or smaller. He doesn't seem to be in pain at all. He can reach it but he hasn't really been messing with it that I have noticed.
I am wondering if this could be a hernia?
It doesn't sound normal, how long have you observed it. It if is stable or reducing in size it may not be a problem.
Does the dog seem to be in pain? Can he reach the area with his mouth, if yes is he giving it a lot of licking or chewing?
I really don't have any idea of what the bump may be, if the puppy is very young it may be some after-birth artifact that will simply go away. Does he eat solid food - look to be several months old, or much younger?