Well, me personally, I think that was a totally appropriate thing for him to do if he was telling the pup, enough is enough. Maybe if you explained to them what he was doing, they would have understood a bit better? Or maybe you did do that.
I think the best way for puppies to learn manners is from other dogs. It bothers me some when owners get freaked out for a dog correcting their puppy for rough play. Not that the boston was being rough, but the in your face attitude thing should be allowed to be corrected as well. Other dogs may not be so nice or gentle. I believe it is better for them to learn from a dog that you know won't hurt them, rather than run the risk with a dog they don't know.
As for him doing it to other dogs? As long as you know, and are positive he won't hurt the other dog, I wouldn't worry about it too much. If you think other people are going to have a huge problem with it, you can try to curb it, but it may also affect how he interacts with others if he is not allowed to tell them to knock it off.