In my teens I had two dogs. One was a large retriever who who immensely tolerant; the kind of dogs that would let kids climb on its back etc.
However, he had the recall of a cat with a full belly, of that makes sense ;) he came back when he was good and ready thank you, you know, when he'd sniffed everything he was interested in, like twigs, poo, that plane on the Sky, every blade of grass...
Consequently, he was rarely, if ever, off the lead. But he was mostly tolerant of dogs that approached him, and people too (the worst he ever did was piss all over someone who didn't ask to stroke him, rolled him on his back to stroke his belly, and, well... I found it funnier than they did). I think cos he was a particularly large retriever, he was pretty confident and not prone to fear or nerves.
Anyway, one day we walking along with both my dogs on their leads, and this Alsatian approaches us and began jumping up on the retriever's back, trying to sniff his bum, and getting increasingly antsy.
After a good ten minutes of this my retriever was starting to get fed up, not aggressive, but clearly not the enjoying it. In spite of my "ffs mate" comments, the owner wouldn't, or couldn't, call it off.
Then the Alsatian began on my Labrador, who was smaller, and while it never bit in its life, it was considerable less confident than my retriever. This was the final straw for my retriever. It wrapped the lead round my legs as bounded past me, knocked the Alsatian on its back to the ground. Then from somewhere in it's gut it growled like I'd not heard him before.
The Alsatian went very quiet. I pulled my dog off it, and it ran back to its owner, who was finally coming over. The owner began with "wtf whys your f'in dog doing that?!" I was young and mouthy, has a sweat at home and walked off.
The point of this laboured story is that there are many reasons why owners have their dogs on leads, and even a usually calm and tolerant dog will react. That dog and it's owner was lucky that my dog had self control. I'm thankful that he did too.
Every owner has a responsibility to make sure their dog doesn't interact with dogs and people in ways that might frighten/provoke them. Don't blame others, take responsibility for yourself.