To some degree, yes. I certainly believe that animals (dogs in particular) can pick up on body language and smells that we do not perceive. Some dogs can "smell" cancer. Some service dogs can sense when their "patient" is going to have a seizure or their blood sugar is too low. How do they do this? Is it a "sense" or a "smell" they pick up? They are still studying trying to figure this out. Dogs also pick up on YOUR cues, even if YOU are unaware you are giving any off.
Our wonderful GSD loves all children, and likely would have behaved much like your dog did with all the kids at that park. Even with the lady who walked over. But she is very cautious and leery of unknown men. She would try to prevent our neighbor kids' dad from coming into our yard to get his own kid. He's virtually a stranger to her, and the kids are her "wards" almost, lol. She would have barked etc at the kids' club man's approach, too. BUT, she would have gotten over it pretty quickly if I was okay with it. Probably. But, there could also have been other things she picked up on that would prevent her from calming down completely.... like happened in the case you describe.
When we first moved into our home (brand new, still getting punch list items taken care of in the first few weeks), I had someone come out to add sometime above our fireplace. Two guys came. An older gentleman and his younger apprentice. Looked pretty much the same, dressed pretty much the same, both complete strangers to me, just one was late teens/maybe 20 and the other was probably 50. My dog did NOT like the younger kid AT ALL. The older guy--meh. She watched him. But the younger kid, she growled at, raised hackles, even snarled once when he tried to reach his arm out in an attempt to "make friends" with her. She sat ON my foot or right in front of my daughter the entire time the men were at our house and never let her attention wander to ANYTHING else--just that kid. That is not her normal behavior. Most strangers she warms up to easily once she sees that I am fine with the person.
Was the kid bad? Maybe, maybe not. Did he have an odor about him that bothered my dog (drug use?)? Maybe, maybe not. Problem is, I'll never know what it was, because my dog can't talk. But I know I would not let that kid inside my house again in the future. And I know that my dog would not let him in either, if we weren't home.
So, I would say, take note. But don't make any kind of accusations because you have no basis for any.