Seems that other dogs could be just as dangerous no matter where they are.
I often wonder when people will realise that no matter how docile your dog may be, it has, as they all do, have a trigger point where they can turn in an instant and follow their defence and attack mode.
The problem is, until that trigger is activated, no one knows what it is, and then it is too late.
Also, just because one dog appears to like every other dog, many other dogs do not like suddenly being approached by an unknown animal, not every dog likes every other dog !!
I have had dogs for a very long time, mainly large breeds, like my Great Dane, but also Bullmastiffs, Mastiffs, Lurchers and more recently Boston Terriers.
Individually they like most things, especially people and are not bothered by other dogs, but when we are all out together, it is a different matter, they are a pack and act as such, and because I know how they act, they are never off the lead when walking together.
But, often a loose dog will run towards us and that is seen as a threat by the pack and as they cannot use their Flight mode and run away, as they are on leads, they go into fight mode and should the loose dog get within reach, they will bite.
I have the advantage of having a local farm where I am the only person allowed to take the dogs onto for exercise and working, but even so, some people who do not have permission get onto the land and let their dogs off the lead, and then get very abusive when told in no uncertain terms to go away.
When they are working and a loose dog appears then they see that as prey and act accordingly, but to educate some people is impossible, but big vets bills seem to resonate and focus their minds.