That guy is an asshole if that is how it played out. Even with my dog, who is always on leash except in off leash parks, I am wary about some people. There's a lady with a cane near our building that always cocks it like she'll clobber any dog that comes near her. Scary stuff. Now for my dog story that ties with similarly with the OP..
Walking around a park while out with my dog (about 44lbs), a small dog (15lbs, maybe?) was off leash and came charging up to us. This happens quite a bit, aggressive small dog off leash, in a place where you are required to have your dog on leash. I always hold my dog at my side and if small dogs, even those being super aggressive, he's pretty calm. Most dogs keep their distance at a few feet and just snarl and bark their heads off before the owner can come leash them.
This time though, the dog comes all the way in and starts trying to bite my dog. So I have to let up on the leash so my dog can maneuver and I'm trying to keep the dog way with my foot, pushing him away and he's basically under my dog trying his damndest to take a bite. The owner is about 15 meters away with another dog (on leash), taking her time getting there. While playing footies with this dog, there's a opening so I give the dog a good boot. I didn't kick it super hard as I didn't want to hurt it, but enough to get it to back off my dog.
The owner predictably flips out and their vantage point is 'It's just a small dog, what harm could it do?'. Well, my dog had been bitten twice in the past and little dogs can take a good chunk out, even if the end result would not end up being life threatening. I felt very bad about having to do that to a dog, but I would have felt much worse if my dog had been bitten again because of a stupid dog owner.
edit: Lots of people saying 'it's only a pug!' seems to be why so many small dog owners seem okay with having their dogs off leash all the time, regardless of their temperament, recall, or laws.