Like tc says, hard to call unless you can observe the dog. There are two schools of thought on letting pups chase birds. I fall in the opposite camp, I don't see any reason to allow a pup to do something if I'm going to have to break him of later.

In your case the pup is pointing and backing, so I sure wouldn't want to mess this up with allowing him to chase birds. Chasing birds can build prey drive, but not necessarily cure the fear of the noise.

It is cause for some concern. If he isn't getting worse, I might do nothing except hunt him. Be sure not to shoot right over him and don't put him in a position where 2 or 3 guys let loose over him. I'd be sure to come in from the side to minimize the muzzle blast over him as well. If he sees mama and brother aren't bothered by the gun, I suspect he will join in the fun.