I agree, one individual, and there may be something going on. Dogs can smell much better than we do. I have heard of a dog reacting to an individual, and days later he was diagnosed with colon cancer. Dogs can smell cancer. Was it a coincidence, though?
The canine brain, amongst its fellows, communicates almost exclusively through body language. Body language tells them the other dog wants to play, or wants nothing to do with you, or is more dominant, or submissive. They are in tune with body language, they are programmed that way. And, fearfulness has it's own smell. Dogs pick up on subtle traces of nervousness. When we are at shows, people will tell you to pop a mint if your nervous because nervousness will come out in your breath to the extent that the dog will notice and become apprehensive.
People who do not like dogs, who are afraid of dogs, who are constantly looking to get something they have no business having may be sending very distinct signals to the dog that we and the person have no clue about. And, people don't want to let you know that they are frightened of your dog, some of them. Or they do not like your dog. The dog knows.
Yeah, if your dog does not like an individual, the individual might not be trustworthy, might have something going on inside that the dog is picking up on, might be anything.
Keep watching your dog, and increase the distance between that person and your dog. Maybe you will never know what the issue is. Maybe in the future you find out he is a pretty notorious dope-addicted burglar that cases the houses of everyone he knows and cleans them out. Probably not. But you never know. If it is just one person, then maybe the dog is picking up on something you haven't.
Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.