It is unfortunate that on your walk you had a run-in with a bully breed dog and that dog was aggressive to your dog. None of us like being in that situation because, quite frankly, we don't know anything about the strange dog that is around us and our dogs. When you see a pack of dogs, being two or more, you can also be sure that this situation can be even more negative because unfortunately it only takes one of those dogs to decide whether it is going to attack your dog and more likely than not, the other dogs with it will join in, even when this is not their usual way of being when alone. This is called "pack mentality.”
Pit bulls are not unpredictable in the least. In fact the dog aggressive situation you found yourself in was very predictable. You were wise to be concerned, as would I have been. The fact there were a few dogs together would have concerned me even more.
With that said, even though a breed trait of the pit bull/bully breed is dog aggressiveness, I know more pitties that are dog friendly and get along with all dogs. Knowing this, I still go with the rule of thumb that if my dogs and I are around an unfamiliar dog, I use caution, regardless of breed. Large dogs can mean a big dog fight; small dogs often instigate fights and insecure under- socialized dogs that have not been given the chance to learn "dog language" can also create fights unfortunately. This is why it's important to have dogs on a leash, and to have control of them and be able to prevent any negative clashes between them.
Unfortunately like so many other negative dog experiences people have, this is not a breed issue, but a lack of responsible ownership issue. The dogs you encountered should all have been on leashes, and this situation would never have happened. This is not the dog's fault, but the owner's fault.
I'm glad your dog is fine and back to normal.
Lisa Day
Sparwood