He may need to witness 'normal' puppy and dog interactions from a distance so that he can get the hang of things himself without being overwhelmed by being suddenly in the middle of things himself. We carried Ollie in arms to the outside of the dog park before his vaccinations kicked in so that he he could watch what the dogs were up to from a distance. And when as a young adult dog he went through a bad period of overreacting to puppies I used to feed him with youtube videos of puppies playing excitedly in the background so that he got a positive association for this without being in the middle of things and possibly terrorising any more pups.
Being on lead can sometimes be hard for pups in this situation too, as they can feel they can not escape and have an escalated reaction because of this, to warn others off because the other option of running away is not available to them.
