So, how is the dog? I hope he is okay.
I would say the proper thing to do would be to just say something to him about it. Ask him why he felt the need to hit your puppy? He may have been really freaked out. Not do defend his actions, I think anyone who would harm a puppy (unless it's self defense) should get a swift kick in the ass, but this is a special case. Besides, it's not like he's going around looking for puppies to kick.
But one does wonder if he lives alone and is running around exposing himself if he should not have some type of care.