Border Collies don't stare at and stalk other dogs. Prey animals, and cats, but not other dogs. That's a neurotic Border Collie you met, and I would bet that its owner is complicit in its emotional state. And why was she allowing that behavior by her dog as she just stood talking to someone? Jerk alert ...
One of my trainers says she has never met so many anxious and fearful dogs as she sees now. It makes sense, though: dogs are the canaries in the coal mine. WE are anxious and stressed to a level we never have been before. We are afraid of other people, of unknown threats, and of our very environment -- and with good reason. Dogs, who are so much more emotionally attuned to their surroundings, of course would reflect that, and share it.
No offense, but anyone who takes the word of someone that their dog is friendly, is not really paying attention. Those dog owners don't know from 'friendly' and as with the BC owner, they will let their dogs engage in all sorts of unwanted, rude and threatening behavior AT THE EXPENSE OF YOUR DOG. I've had people tell me they think donald trump will be a fine President, and my eye-rolling response is the same as my response to 'oh, my dog is friendly!' 'You're a delusional nitwit, get away from me' is how I would summarize it.
In the nature preserve where I go frequently with my dogs, members' dogs can be off-leash if they are under voice control. It's rare that we meet other dogs out there, but even once or twice encountering someone who thinks that 'under voice control' means shouting their dog's name eighty-five times as the dog bounds around riling up my dogs has made me wary. Now, whenever we see another dog and owner at the preserve, I ostentatiously step OFF the trail, call all my dogs around me, and put them on sits that I reward with treats until the other dog and owner are past us. The people who know us just say hi and keep going, the people who don't know us might say 'oh, my dog is friendly!' thinking I will release my dogs, but I don't. I say 'how nice for you, we are working here' and we let them get out of sight before I release my dogs back to the trail.
I wish I could take the word of people who say 'oh, my dog is friendly!' but I can't. And I won't make my dogs pay the price for that.