I wonder if this was a dog park? I never go to them (too worried about bad dogs) but if so I suppose the dogs are allowed to be off leash.
We went to one and it turned out that our dog was the bad dog. All the other dogs were either playing fetch with their owners or running around together in a well-behaved manner.
Our dog (mid-sized) hadn't been around other dogs very much and a few times he over-reacted when approached by other dogs even though they obviously just wanted to play.
It seemed to me that the dogs who were regulars at this park were socialized to get along, which is probably the behavior enforced by their owners. We were obviously causing a disruption so we left.
I’ve never taken dogs to dog parks. It’s a good place for dogs to pick up viruses and parasites.